Organic electro luminescense display apparatus and application thereof

ABSTRACT

A technology for reducing the so-called “phosphor burn-in” phenomenon where the variation of luminance arises by reducing display luminance of a certain pixel caused by deterioration in a display apparatus constituted by an organic electro luminescence element is provided. In the display apparatus, when displaying an image acquired by an image acquiring unit, luminance substantially same as average luminance of the acquired image is set to a non-display area where the image is not displayed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application and claims the prioritybenefit of Patent Cooperation Treaty Application Number PCT/JP03/02503,filed on Mar. 4, 2003, which in turn claims the priority benefits ofJapanese Patent Application Number JP2002-057467, filed on Mar. 4, 2002,Japanese Patent Application Number JP2002-079418, filed on Mar. 20,2002, Japanese Patent Application Number JP2002-089126, filed on Mar.27, 2003, Japanese Patent Application Number JP2002-089127, filed onMar. 27, 2003, Japanese Patent Application Number JP2002-089707, filedon Mar. 27, 2003, and Japanese Patent Application Number JP2002-090017,filed on Mar. 27, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display method and a displayapparatus, and it particularly relates to a technology for averagingdegradations of each optical element in an active matrix type organicelectro-luminescence display apparatus and reducing variation ofluminance thereof.

2. Description of the Related Art

Organic electro-luminescent displays (hereinafter, also referred to as“organic EL displays” or “organic EL panels”) are attracting attentionas new flat-type displays. In particular, active matrix type organic ELdisplays having thin film transistors (hereinafter, also referred to as“TFTs”) as switching elements are regarded as sweeping out the currentlyprevailing liquid crystal displays in the near future, and are in afierce development race for practical use.

Unlike liquid crystal displays, organic EL displays have self-luminouselements. This eliminates the need for a backlight which isindispensable to liquid crystal displays, promising apparatuses of yetlower profile and lighter weight. Moreover, organic EL panels areexpected for application as a light emitting devices such as thebacklight of liquid crystal displays using a self-luminouscharacteristic.

It is known that, as for the organic EL element, degradation progresseswith luminescence and luminance thereof gradually decreases. Developmentof the organic luminescent material which does not deteriorate easily isimportant for providing the organic EL panel with high display qualityand long life, of course, but it is unescapable that degradation withthe passage of time arises for the organic EL element. The first thingto do is development of the technology for suppressing the influence ofthe degradation to the minimum at a present stage.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoingcircumstances and an object thereof is to provide a technology forimproving display quality of a display apparatus.

An embodiment of the present invention relates to a display method. Inthis display method, when displaying an image on a display area narrowerthan an area which can be displayed, luminance data of a non-displayingarea which does not display the image among the area which can bedisplayed is set as a guessed value of an average luminance of theimage. “An area which can be displayed” means a whole display screen inthe display apparatus, and “a display area” means an area where an imageas an object of display is actually displayed among the area which canbe displayed. “A non-displaying area” means an area other than thedisplay area among the area which can be displayed. “Non-displaying”means that the image as an object of display is not displayed, and doesnot necessarily mean that nothing is displayed. The degradation speed ofthe display element which constitutes each pixel can be averaged overthe whole screen and the variation in the display luminance resultingfrom the variation in degradation speed can be reduced, by making theaverage luminance of the image displayed on the display area and theaverage luminance of the image displayed on the non-displaying areabecome almost the same.

Another embodiment of the present invention relates to a displayapparatus. This display apparatus comprising: an acquisition unit whichacquires a first image to be displayed; a first setting unit which setsa first area in which the first image is displayed and places the firstimage on the first area; and a second setting unit which sets, when thefirst area is smaller than an area which can be displayed, a secondimage to be displayed on a second area in which the first image is notdisplayed; wherein said second setting unit sets the second image in amanner where a guessed value of an average luminosity of the first imageis substantially same as a guessed value of an average luminosity of thesecond image. The average luminance of a general image may be guessedbeforehand, and thus guessed average luminance may be made become almostthe same as the average luminance of the second image. The luminance ofmore than 30% and less than 40%, or more favorably more than 30% andless than 35%, for example, of the maximum luminance may be adapted asthe average luminance of the general picture.

The second setting unit may calculate the average luminance of the firstimage and may set the second image whose average luminance issubstantially same as calculated average luminance of the first image tothe second area. The degradation speed of the display elements can beaveraged with higher accuracy by selecting the second image according tothe average luminance of the first image whenever the first image isdisplayed.

Further another embodiment of the present invention also relates to adisplay apparatus. This display apparatus comprising: an acquisitionunit which acquires a first image to be displayed; a first setting unitwhich sets a first area in which the first image is displayed and placesthe first image on the first area; a second setting unit which sets,when the first area is smaller than an area which can be displayed, asecond image to be displayed on a second area in which the first imageis not displayed; a first storing unit which stores an accumulativeaverage luminance of the first image previously displayed on the firstarea; and a second storing unit which stores an accumulative averageluminance of the second image previously displayed on the second area;wherein said second setting unit sets the second image in a manner wherethe accumulative average luminance of the second image approaches theaccumulative average luminance of the first image. Though the averageluminance of each first image differs from the average luminance of eachsecond image somewhat, it does not necessarily lead to the variation inthe display luminance immediately. These average luminance should justbecome almost the same for long term. The accumulative average luminanceof the first images and second images may be stored, and the secondimage may be adjusted to make these accumulative average luminancevalues become almost the same for long term. The variation in thedisplay luminance can be reduced by this method. According to thismethod, grater flexibility of a display can be achieved. For example,the second image can be selected based on the color or theme of thefirst image.

The second image may be an image in which all pixels have the almostsame luminance data. That is, the second image may be an image whichconsisted of only one color. In this specification, the word an “image”is used, even if the image consists of only one color.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses andsystems may also be practiced as additional modes of the presentinvention.

This summary of the invention does not necessarily describe allnecessary features so that the invention may also be a sub-combinationof these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

The object described above, other objects, characteristics andadvantages will be appreciated by referring to the preferred embodimentsand associated drawings.

FIG. 1 is a figure showing an internal structure of a mobile terminalaccording to a first example of a first embodiment.

FIG. 2 is a figure showing a state where a display area is set up in thecenter of an area of a display unit which can be displayed, and an imageis displayed.

FIG. 3 is a figure showing a state where average luminance data of ageneral image is set up to a non-display area.

FIG. 4 is a figure showing a circuit structure of a single pixel of thedisplay unit.

FIG. 5 is a figure showing an internal structure of a mobile terminalaccording to a third example of the first embodiment.

FIG. 6 is a figure showing an example of an internal data of anaccumulated average luminance storing unit.

FIG. 7 is a block diagram showing a structure of a cellular phoneaccording to a second embodiment.

FIGS. 8A and 8B are figures for explaining a black character displaymode and a white character display mode.

FIG. 9 is a flowchart showing an example of a procedure of changing amode.

FIG. 10 is a flowchart showing another example of a procedure ofchanging a mode.

FIG. 11 is a figure showing a basic structure of an organic EL display.

FIG. 12 is a circuit diagram of a single pixel of an active matrix typeorganic EL display.

FIG. 13 is a block diagram showing a schematic structure of a cellularphone.

FIGS. 14A, 14B, 14C, 14D, and 14E are schematic diagrams showing fivesteps of a specific picture used for displaying residual quantity of abattery.

FIG. 15 is a schematic diagram showing an example of initial display incase where display luminance of a rightmost bar is set up lowest, aleftmost bar highest, and a mean value of them is set up as displayluminance of a central bar, in the battery residual quantity picture.

FIGS. 16A and 16B are graphs showing a change over time of displayluminance of a rightmost bar which has high probability to light (solidline) and a change over time of display luminance of a leftmost barwhich has low probability to light (doted line).

FIGS. 17A, 17B, 17C, 17D, and 17E are schematic diagrams showing fivesteps of a specific picture used for displaying antenna picture.

FIG. 18 is a schematic diagram showing an example of initial display incase where display luminance of a leftmost bar is set up lowest, arightmost bar highest, and a mean value of them is set up as displayluminance of a central bar, in the antenna picture.

FIGS. 19A, 19B, and 19C are schematic diagrams showing dots constitutinga first picture (bar) and dots constituting a second picture (characterof “charge”) in the battery residual quantity picture.

FIG. 20 is a schematic diagram showing pictures which can be displayedon upper part of a color organic EL display.

FIG. 21 is a figure showing a basic structure of an organic EL displayapparatus.

FIG. 22 is a figure showing a state where a character is shifted anddisplayed.

FIGS. 23A, 23B, and 23C are figures showing a method of shifting animage and a change of dots constituting a pixel when being shifted.

FIG. 24 is a figure showing a relation between a display area and aneffective display area.

FIG. 25 is a figure showing a display area of one font.

FIG. 26 is a structure diagram of an organic EL display apparatusaccording to an embodiment.

FIGS. 27A, 27B, and 27C are figures showing a state where a displayimage is scrolled.

FIGS. 28A and 28B are figures showing a state where mosaic processing iscarried out to a display image.

FIGS. 29A and 29B are figures showing a state where a display color of adisplay image is changed at a fixed timing.

FIGS. 30A, 30B, and 30C are figures showing a state where luminanceratio of RGB is gradually changed when changing a display color of adisplay image.

FIG. 31 is a flowchart showing a procedure of changing a display colorto average grade of degradation of OLED.

FIG. 32 is a flowchart showing a procedure of performing adjustment to adisplay image according to grade of degradation of OLED.

FIG. 33 is a figure showing a display screen of a cellular phone inwhich a display area is divided into three areas of up, middle, anddown.

FIG. 34 is a figure showing how a display image shifts.

FIG. 35 is a structure diagram of a cellular phone as an organic ELdisplay apparatus according to an embodiment.

FIG. 36 is a figure showing relation between a display image which isdisplayed on an organic EL panel and is not scrolled, and a memoryspace.

FIGS. 37A and 37B are figures showing a procedure of reading image databy a timing control IC.

FIGS. 38A and 38B are figures showing a display screen in which aphosphor burn-in is arisen.

FIGS. 39A and 39B are figures showing a display screen in which acharacter string is displayed with two kinds of fonts different fromeach other.

FIGS. 40A and 40B are figures showing a display screen in which acharacter string is displayed with two size of font, large and small.

FIG. 41 is a figure showing a state where a color of an area where acharacter string is not displayed is gradually changed from a backgroundcolor to a display color of the character string.

FIGS. 42A and 42B are figures showing a state where a character isshifted in a pixel area which forms one font.

FIG. 43 is a structure diagram of an organic EL display apparatusaccording to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on the preferred embodiments.This does not intend to limit the scope of the present invention, butexemplify the invention.

FIRST EMBIDIMENT

[Example of the First Embodiment]

FIRST EXAMPLE

In the present embodiment, in order to average degradation speed ofdisplay elements which constitute pixels of a display apparatus on thewhole screen, and to reduce variation in display luminosity resultingfrom variation in degradation speed, when displaying an image, an areawhere the image is not displayed is displayed in a color of about 30% ofwhite which is assumed as average luminance of a general image.

FIG. 1 shows an internal structure of a mobile terminal 10, as anexample of a display apparatus of the present embodiment. The mobileterminal 10 mainly comprises a communication unit 20, a control unit 30,a memory unit 40, a display unit 100, an input unit 50, a microphone 60,and a speaker 70. The communication unit 20 includes an antenna 22 whichtransmits and receives a signal, a receiving unit 24 which decodesreceived signal, and a transmitting unit 26 which modulates andtransmits data. The communication unit 20 controls communication withother apparatus via a cellular phone network. The display unit 100displays text information, image information and the like. In thisembodiment, an organic EL panel is used as the display unit 100. Thedisplay unit 100 may be an inorganic EL panel or a liquid crystal paneland the like. The technology of this embodiment is especially suitablefor the organic EL panel with which degradation of the display elementposes a problem. The input unit 50 receives input information fromoutside via a keyboard, mouse, button, and the like. The microphone 60inputs audio information from outside. The speaker 70 outputs audioinformation to outside.

The control unit 30 controls of the mobile terminal 10 as a whole andperforms various processings required for a display. In terms ofhardware, this structure can be realized by a CPU, a memory and otherLSIs of an arbitrary computer. In terms of software, it is realized bymemory-loaded programs or the like having a function of controllingdisplay, but drawn and described here are functional blocks that arerealized in cooperation with those. Thus, it is understood by theskilled in the art that these functional blocks can be realized in avariety of forms by hardware only, software only or the combinationthereof.

The image acquiring unit 32 acquires an image to be displayed fromoutside via the communication unit 20 or by reading out the image storedin the memory unit 40. The display area setting unit 34 sets an area todisplay the image inside an area which can be displayed in the displayunit 100 according to the size of the acquired image. The non-displayarea setting unit 36 sets an image to be displayed on an area other thanthe display area among the area which can be displayed, that is, anon-display area in which the acquired image is not displayed. Thedisplay control unit 38 places the image acquired by the image acquiringunit 32 on the area set by the display area setting unit 34, and setsthe image set by the non-display area setting unit 36 to the non-displayarea around the display area. The display control unit 38 thus generatesthe image data of the display screen and writes it to the graphicsmemory 42. Then, the display control unit 38 outputs the image data andthe driving signal to each pixel of the display unit 100 at thepredetermined timing.

FIG. 2 shows a state where the display area 104 is set up in the centerof the area 102 which can be displayed of the display unit 100, and theimage is displayed. In the example shown in FIG. 2, the display area 104is set up in the center of the area 102 which can be displayed todisplay the image, and the non-display area 106 is set around thedisplay area 104, because the size of the image is smaller than the area102 which can be displayed. It is favorable, considering a viewpoint ofreduction of the power consumption and reduction of the degradation ofthe organic EL element constituting each pixel, that the luminance ofthe non-display area 106 is set zero, that is, blackout. If an image isdisplayed on the display area 104 for a long time, however, since thetime in which the pixel of the display area 104 is on becomes long ascompared with the pixel of the non-displaying area 106, degradation ofthe organic EL element in the display area 104 will progress earlier,and luminance will decrease. As a result thereof, even if the wholescreen is displayed with the same luminance data, the luminance of theorganic EL element near center of the screen will become lower than theluminance of the organic EL element near end of the screen, and a partnear center of the screen will be displayed darkly. Especially, whendisplaying the image of the same size frequently, as a result ofcontinuing displaying an image on the same display area 104 for a longtime, the pixel in the display area 104 deteriorates earlier thansurrounding pixels and the luminance thereof decreases. Consequently,the so-called “phosphor burn-in” phenomenon will happen in which therectangle of the display area 104 is seen when displaying an image onthe whole screen.

In this embodiment, to reduce generating such a phenomenon, thenon-display area setting unit 36 displays the non-display area 106 incolor of about from 30% to 35% of white which is a guessed averageluminance level of the general image to make the organic EL element inthe non-display area 106 deteriorate to the same extent as the organicEL element in the display area 104. Thereby, the degradation speed ofthe organic EL element in a whole screen can be averaged and thevariation in the luminance and the phosphor burn-in phenomenon can bereduced. By reducing the variation in the luminance and phosphorburn-in, it contributes also to an improvement of the life of thedisplay unit 100.

FIG. 3 shows a state where an image having average luminance of ageneral image is set up to a non-display area. In this example, theimage constituted by one color of about 30% of white is set up to thenon-display area 106. However, the image which has arbitrary colors andpatterns may be set as long as the average luminance thereof is about30% of white. In the case where the patterned image is displayed on thenon-display area 106, two or more images whose average luminance isabout 30% of white should be prepared. The image should be replacedsuitably and displayed to prevent the phosphor burn-in of the image.

FIG. 4 shows a circuit structure of a single pixel of the display unit100. This circuit comprises an organic light emitting element OLED, twotransistors Tr1 and Tr2 for controlling the organic light emittingelement OLED, a capacitor C, a scan line SL which transmits a scansignal, a data line DL which transmits a luminance data, and a powersupply line Vdd which supplies current to the organic light emittingelement.

The power supply line Vdd supplies an electric current for making theorganic light emitting element OLED emit. The data line DL transmitsluminance data for controlling luminance of each of the organic lightemitting elements OLED. The scanning line SL transmits scan signals forcontrolling the emitting timing of each of the organic light emittingelements OLED. The luminance data and the scan signal are supplied bythe display control unit 38.

A gate electrode of a first transistor Tr1 (hereinafter also referred toas “switching transistor”) is connected to the scanning line SL. A drainelectrode (or a source electrode) of the switching transistor Tr1 isconnected to the data line DL. A source electrode (or a drain electrode)of the switching transistor Tr1 is connected to a gate electrode of asecond transistor Tr2 (hereinafter also referred to as “drivingtransistor”). In this embodiment, the switching transistor is adouble-gate transistor having two gate electrodes. In anotherembodiment, the switching transistor may be a single-gate transistor ora multi-gate transistor having three or more gate electrodes. Theswitching transistor Tr1 may be an n-channel transistor or a p-channeltransistor.

A source electrode (or a drain electrode) of the driving transistor Tr2is connected to an anode of the organic light emitting element OLED. Adrain electrode (or a source electrode) of the driving transistor Tr2 isconnected to the power supply line Vdd. Similar to the switchingtransistor Tr1, the driving transistor Tr2 may be a single-gatetransistor or a multi-gate transistor, and may be an n-channeltransistor or a p-channel transistor.

An anode of the organic light emitting element OLED is connected to thesource electrode (or the drain electrode) of the driving transistor Tr2.A cathode of the organic light emitting element OLED is connected toground potential. An electrode of the capacitor C is connected to thedrain electrode (or the source electrode) of the switching transistorTr1 and the gate electrode of the driving transistor Tr2. Anotherelectrode of the capacitor C is connected to ground potential via a wirenot shown in figures, or may be connected to the power supply line Vdd.

An operation of the circuit structured as described above is explainedhereinbelow. As the scan signal of the scanning line SL goes high forwriting the luminance data to the organic light emitting element OLED,the switching transistor Tr1 turns on, the luminance data which is beinginputted to the data line DL is set in the driving transistor Tr2 andthe capacitor C. A current which corresponds to the luminance data thusflows between the source electrode and the drain electrode of thedriving transistor Tr2, and this current flows in the organic lightemitting element OLED, so that the organic light emitting element OLEDemits. When the scan signal of the scanning line SL becomes low, theswitching transistor Tr1 turns off, but the gate voltage of the drivingtransistor Tr2 is maintained, so that the organic light emitting elementOLED continues emitting according to the set luminance data.

At the next emitting timing, the scan signal of the scanning line SLbecomes high again, the switching transistor Tr1 turns on, then the newluminance data which is inputted to the data line DL is set in thedriving transistor Tr2 and the capacitor C. Thereby, the organic lightemitting element OLED emits corresponding to the new luminance data.

SECOND EXAMPLE

In this example, when the mobile terminal acquires the image to bedisplayed, the mobile terminal calculates average luminance of the imageand selects an image to be displayed on the non-display area based onthe average luminance. The internal structure of the mobile terminalaccording to this example is similar to the first example shown inFIG. 1. Hereinafter, a structure differing from that in the firstembodiment will be mainly described.

The non-display area setting unit 36 calculates the average luminance ofthe image acquired by the image acquiring unit 32. The average luminancemay be calculated for every signal of R, G, and B. The non-display areasetting unit 36 may calculate the average luminance of luminance signalY. The non-display area setting unit 36 displays an image whose averageluminance is substantially the same as the calculated average luminance.The image may be an image may be covered with the average luminosityvalue or an image with pattern which is prepared in the memory unit 40beforehand. In the case of the patterned image, the phosphor burn-in ofthe image can be prevented by replacing two or more images suitably anddisplaying.

THIRD EXAMPLE

In this example, an accumulated average luminance of images displayed onthe display area and an accumulated average luminance of imagesdisplayed on the non-display area are stored, and the mobile terminaladjusts the images so that these accumulated average luminance valuesbecome almost the same for a long term.

FIG. 5 shows an internal structure of the mobile terminal 10 accordingto the third example. The mobile terminal 10 of the present examplefurther comprises an accumulated average luminance storing unit 44 inaddition to the structure of the mobile terminal 10 of the first exampleshown in FIG. 1. Hereinafter, a structure differing from that in thefirst embodiment will be mainly described.

When the image acquiring unit 32 acquires an image to be displayed, thenon-display area setting unit 36 calculates the average luminance of theimage. The non-display area setting unit 36 reads out the accumulatedaverage luminance of the display area and the accumulated averageluminance of the non-display area for the display area from theaccumulated average luminance storing unit 44 according to the size ofthe image. The non-display area setting unit 36 selects an image to bedisplayed on the non-display area so that these accumulated averageluminance values can approach. For example, when the accumulated averageluminance of the display area is lower than the accumulated averageluminance of the non-display area, the image whose average luminance ishigher than the average luminance of the image to be displayed this timeis set as the non-display area. Thereby, the average luminance of thedisplay area and the non-display area can be averaged in a long term.The non-display area setting unit 36 re-calculates the accumulatedaverage luminance using the average luminance of the image displayedthis time and the average luminance of the image displayed on thenon-display area, and stores thus calculated accumulated averageluminance in the accumulated average luminance storing unit 44. When adisplay image is a still image, the accumulated average luminance may becalculated in consideration of display time.

FIG. 6 shows an internal data of the accumulated average luminancestoring unit 44. In the accumulated average luminance storing unit 44,an area ID column 110, a display area size column 112, a display areaaccumulated average luminance column 114, and a non-display areaaccumulated average luminance column 116. For example, when the size ofthe image acquired by the image acquiring unit 32 is 100 dots by 100dots, the information of the record of area ID “1” is read by thenon-display area setting part 36. Since the accumulated averageluminance of the display area of area ID “1” is “70.5” and theaccumulated average luminance of the non-display area is “70.3”, theaverage luminance of the non-display area should just set up higher thanthe average luminance of the display area in this time. The non-displayarea setting unit 36 may adjust so that the accumulated averageluminance of the display area and the non-display area may become equalby one display. The non-display area setting unit 36 may adjust so thatthe accumulated average luminance of the display area and thenon-display area may become gradually equal by two or more displays.

The flexibility of the image set as the non-display area spreadsaccording to this method. For example, when displaying a photograph andthe like, a frame may be displayed around the photograph. Surroundingimage can be selected according to the kind or color of the imagedisplayed or taste of a user. When displaying an animation on thedisplay area, if the average luminance of a surrounding image is changedaccording to change of the average luminance of the animation, there isa possibility that the screen becomes hard to see. In this case, theimage displayed on the non-display area may be fixed with the image setup first, and the accumulated average luminance of the display area andthe non-display area may be calculated and stored when the display ofthe animation is completed. In the next display, the accumulated averageluminance should just be adjusted so that they can approach.

Above-mentioned embodiments are only exemplary. It is understood bythose skilled in the art that there exist other various modifications tothe combination of each component and process described above and thatsuch modifications are encompassed by the scope of the presentinvention.

In this embodiment, explanation is made taking the case of the mobileterminal as the display apparatus. The technology of the presentinvention is not limited in this, however, and can also be applied tothe arbitrary display apparatus like the television, the display of thecomputer.

[Effect of the First Embodiment]

The variation in luminance of a display apparatus can be reduced anddisplay quality can be improved according to this embodiment.

SECOND EMBODIMENT

[Field of the Second Embodiment]

The present embodiment relates to a mobile terminal comprising anorganic EL (Electro Luminescence) display apparatus.

[Related Art of the Second Embodiment]

In recent years, development of an organic EL display is progressing.For example, adopting the organic EL display as a display of a cellularphone is in the air.

As shown in FIG. 11, an organic layer 213 is formed on a glass substrate211 by arranging an organic hole transport layer 215 and an organicelectron transport layer 216 on both sides of the organic luminescencelayer 214. An organic EL panel is formed by arranging an anode 212 and acathode 217 on both sides of the organic layer 213. The organicluminescence layer 214 emits light by applying a predetermined voltagebetween the anode 212 and the cathode 217.

The anode 212 is made with transparent ITO (Indium Tin Oxide). Thecathode 217 is made with Al—Li alloy for example. They are formed stripetype and arranged in the direction which crosses mutually configuring amatrix.

The anode 212 is used for a data electrode, and the cathode 217 is usedfor a scanning electrode, for example. In the state where one scanningelectrode placed horizontally is selected, a voltage according to aninput data is applied to each data electrode placed perpendicularly.Then the organic layer 213 emits light at the intersection of theseelectrodes and one line is displayed. The scanning electrode is scannedby switching perpendicularly one by one, and one field is displayed.

An active matrix type driving mode is known as the driving mode of theorganic EL display, in which luminescence of each pixel is continuedover one vertical scanning term, other than the above-mentioned passivematrix type driving mode in which the time division driving is performedusing the scanning electrode and the data electrode.

In the active matrix type organic EL display, each pixel 252 comprisesan organic EL element 250 constituted by a part of the organic layer, adriving transistor TR2 which controls current supply to the organic ELelement 250, a writing transistor TR1 which turns on by being applied ascanning voltage SCAN from the scanning electrode, and a capacitorelement C which holds charge by being applied a data voltage DATA fromthe data electrode when the writing transistor TR1 turns on, as shown inFIG. 12. The output voltage of the capacitor C is applied to a gate ofthe driving transistor TR2.

At first, a voltage is applied to each scanning electrode, then thefirst transistors Tr1 connected to this scanning electrode turns on. Thedata voltage (input signal) is applied to each data electrodesynchronizing with this scan. The data voltage is held in the capacitorC at this time, because the first transistor TR1 is on.

The operating state of the second transistor TR2 is determined by thecharge quantity held in this capacitor C. When the second transistor TR2turns on, for example, current according to the data voltage is suppliedto the organic EL element via the second transistor TR2. Consequently,The organic EL element 250 emits light with brightness according to thedata voltage.

By the way, in the organic EL display, the luminescence characteristicof the organic EL element deteriorates with progress of luminescencetime, the luminance obtained by the same input current may decreaseconsequently. In a cellular phone comprising the organic EL display, theluminescence frequency of pixels in a fixed area always becomes highwhen displaying a character of an e-mail on a screen. Thereby, theluminescence characteristic of these pixels deteriorate remarkablycompared with other pixels. The problem so-called “phosphor burn-in” mayarise as a result.

[Summary of the Second Embodiment]

The object of the present embodiment is to solve a problem of the“phosphor burn-in” with simple structure in a cellular phone comprisingan organic EL display.

The mobile terminal according to this embodiment comprises an imageprocessing circuit which can switch a display mode between a blackcharacter display mode in which a character part is displayed in blackor a color with luminosity lower than that of a background part and thebackground part is displayed in white or a color with luminosity higherthan that of the character part, and a white character display mode inwhich the background part is displayed in black or a color withluminosity lower than that of the character part and the character partis displayed in white or a color with luminosity higher than that of thebackground part, when displaying an electric mail on an organicelectro-luminescence display apparatus; and a control circuit whichcontrols an operation of said image processing circuit; wherein saidcontrol circuit alternately switches the display mode between the blackcharacter display mode and the white character display mode.

The control circuit may instruct a mode switch between the blackcharacter display mode and the white character display mode inaccordance with a predetermined rule in the concrete. As a predeterminedrule, the rule of changing the mode between a display of transmittedmail and a display of received mail, and the rule of changing the modewith a fixed cycle are employable, for example.

The control circuit may switch the mode at a random timing.

The mode switching described above can be achieved by simple change ofthe control program.

In the mobile terminal according to the present invention, the blackcharacter display mode in which a character is displayed with lowerluminance and the white character display mode in which a character isdisplayed with higher luminance can be switched with a predeterminedcycle, at a predetermined timing according to an operation of a user, orat a random timing. Thereby, the situation where only the pixel in afixed area always emits light with high luminance can be avoided, andthe problem of “phosphor burn-in” can be solved.

[Example of the Second Embodiment]

Hereinafter, an embodiment in which the present invention is carried outto the cellular phone will be concretely explained making reference todrawings.

As shown in FIG. 7, the mobile telephone of the present embodimentcomprises a transmission and reception circuit 202, an image processingcircuit 203 for displaying an electronic mail received or to betransmitted by the transmission and reception circuit 202 on an organicEL display 201, a driving circuit 204 which drives the organic ELdisplay 201 in response to an image signal from the image processingcircuit 203, and a control circuit 205 consisted of a micro computerwhich controls operations of the transmission and reception circuit 202and the image processing circuit 203.

FIG. 9 shows procedures performed in case the control circuit 205displays an e-mail on the organic EL display 201. At first, it is judgedwhether an electronic mail to be displayed is transmitted mail or not,at the step S1.

If the mail to be displayed is a transmitted mail, a black characterdisplay mode in which a character part is displayed in black and abackground part is displayed in white is set as shown in FIG. 8A, andthe control circuit 205 supplies a mode switching signal to the imageprocessing circuit 203, at the step S2.

On the other hand, if the mail to be displayed is a received mail, awhite character display mode in which a character part is displayed inwhite and a background part is displayed in black is set, and thecontrol circuit 205 supplies a mode switching signal to the imageprocessing circuit 203, at the step S3 of FIG. 9.

The transmitted mail is displayed in the black character display mode onthe organic EL display 201 as shown in FIG. 8A, and the received mail isdisplayed in the white character display mode on the organic EL display201 as shown in FIG. 8B, consequently.

FIG. 10 shows other procedures performed in case the control circuit 205displays an e-mail on the organic EL display 201. At first, it is judgedwhether today is even-numbered day or not, at the step S11.

If today is even-numbered day, a black character display mode in which acharacter part is displayed in black and a background part is displayedin white is set as shown in FIG. 8A, and the control circuit 205supplies a mode switching signal to the image processing circuit 203, atthe step S12.

On the other hand, if today is odd-numbered day, a white characterdisplay mode in which a character part is displayed in white and abackground part is displayed in black is set, and the control circuit205 supplies a mode switching signal to the image processing circuit203, at the step S13 of FIG. 10.

The transmitted mail and the received mail are displayed in the blackcharacter display mode on the organic EL display 201 at even-numberedday as shown in FIG. 8A, and displayed in the white character displaymode on the organic EL display 201 at odd-numbered day as shown in FIG.8B, consequently.

In the mobile telephone of the present embodiment, since the blackcharacter display mode and the white character display mode are switchedby whether an E-mail is a transmitted mail or a received mail, orwhether today is an even-numbered day or an odd-numbered day, theluminance of pixels which constitute the organic EL display 201 can beaveraged in time over the whole screen, and deviation of the luminancecan be reduced. Consequently, the “Phosphor burn-in” resulting from onlysome pixels carrying out age degradation early can be prevented.

Moreover, in a conventional mobile telephone which always displays acharacter part in black and a background part in white, the powerconsumption of the organic EL display was large because the whitebackground part occupies larger area than the black character part. Inthe mobile telephone of the present embodiment, however, the powerconsumption can be reduced because the black character display mode andthe white character display mode can be switched.

Each component of the present invention is not limited to theabove-mentioned embodiment. Various changes can be made withoutdeparting from the scope of the technology which is described in theclaims.

Various changing rules are employable, for example: a rule in which theblack display mode and the white display mode are switched every timethe power of the cellular phone is turned on; a rule in which the modeis switched every time a mail screen is displayed; a rule in which themode is switched between a case of writing mail and a case of readingmail; a rule in which the mode is switched for every time orpredetermined number of times on the occasion of a display of a mail atthe time of mail creation; a rule in which the mode is switched forevery time or predetermined number of times on the occasion of a displayof a mail which has already been received or transmitted. Moreover, thestructure where the mode is switched at a random timing withoutfollowing a predetermined rule can be adopted.

[Effect of the Second Embodiment]

The “phosphor burn-in” problem can be solved with simple component by amobile terminal comprising an organic EL display according to thepresent embodiment.

THIRD EMBIDIMENT

[Field of the Third Embodiment]

The present embodiment relates to a method for displaying a specificpicture (a picture writing) called “PICT” like an antenna picture, apicture showing residual quantity of a battery, and the like, in acellular phone comprising an organic EL (Electro Luminescence) display.

[Related Art of the Third Embodiment]

In a color organic EL display, one color pixel is constituted by threekinds of organic EL elements (R luminescent element, G luminescentelement, and B luminescent element) which emit R, G, and B lightrespectively. The luminescent elements deteriorates and luminancethereof decreases, if the color organic EL display is used over a longterm. Especially, if large current is continuously supplied to theluminescent element, that is, the luminescent element continuously emitslight with high luminance, the speed of reduction of luminance becomeshigh.

[Summary of the Third Embodiment]

The object of this embodiment is to provide a display method of aspecific picture that can make hard to be conspicuous in luminancedegradation with displaying the picture.

A display method according to the first aspect of the present embodimentis a display method of a specific picture which is displayed on a colororganic EL display and a lighting part thereof increases or decreasesaccording to a situation, wherein the higher a probability of lightingof a part, the lower luminance of the part is set beforehand.

A display method according to the second aspect of the presentembodiment is a display method of the specific picture according to thefirst aspect, wherein the specific picture is a picture showing anantenna and/or a picture showing residual quantity of a battery.

A display method according to the third aspect of the present embodimentis a display method of a specific picture which is displayed at areaswhich overlie each other on a color organic EL display, in which two orthree kinds of the specific picture in roughly classification areswitched and displayed according to a situation, wherein a dot whichconstitutes each specific picture is set up in a manner where a color ofan emitting element turned on differs mutually among the two or threekinds of the specific picture.

A display method according to the fourth aspect of the presentembodiment is a display method of the specific picture according to thethird aspect, wherein the specific picture is a picture of an antennawhich is switched between a first picture showing an antenna bar and asecond picture showing a character showing outside an area where anelectric wave reaches.

A display method according to the fifth aspect of the present embodimentis a display method of the specific picture according to the thirdaspect, wherein the specific picture is a picture showing residualquantity of a battery which is switched between a first picture showinga bar showing the residual quantity of the battery and a second pictureshowing a character showing a charge.

A display method according to the sixth aspect of the present embodimentis a display method of a plurality of specific pictures which isdisplayed on a color organic EL display, wherein the higher a frequencyof displaying a pixel is, the lower luminance of the pixel is setbeforehand.

[Example of the Third Embodiment]

Hereinafter, an example where the present invention is adopted to acellular phone comprising a color organic EL display will be explainedwith reference to drawings.

FIG. 13 shows a schematic structure of a cellular phone. An MPU 3109controls a cellular phone as a whole. An antenna 3101 transmits andreceives an electric wave. A transmitter-receiver unit 3102 receives theelectric wave and transmits the received content to the MPU 3109. Thetransmitter-receiver unit 3102 transmits a transmission signal outputtedfrom the MPU 3109 with the electric wave.

A microphone 3101 communicates an audio signal to the MPU 3109. Aspeaker 3104 outputs an audio signal outputted from the MPU 3109 as asound. A first camera 3105 is a camera attached in the front of a mainbody of the cellular phone in which a color organic EL display 3114 isformed, and transmits shot image to the MPU 3109. A second camera 3106is a camera attached in the back of the cellular phone, and transmitsshot image to the MPU 3109. At a shooting mode, an image shot by thecamera 3105 or 3106 is displayed on the color organic EL display 3114instead of a display image at a normal mode.

An operating unit 3108 is comprised in the main body of the cellularphone, includes various buttons and various switches. In a flash memory3110, data which should be saved when a power turns off are stored.

In a graphics memory 3112, image data to be displayed on the display isstored. Image data is written at the predetermined address in thegraphics memory 3112 based on the image data and a write control signaloutputted from the MPU 3109. Pixel data of the pixel corresponding witha display cycle of the color organic EL display is outputted from thegraphics memory 3112 according to a scan timing.

A timing control IC 3113 supplies a drive signal to the organic ELdisplay 3114 with the image data, and displays an image on the colororganic EL display 3114.

In the color organic EL display 3114, a single color pixel isconstituted with three kinds of organic EL elements (R luminescentelement, G luminescent element, B luminescent element) which emit lightin R, G, B, respectively. Such a color organic EL display 3114 includesthe organic EL element for each color luminescence of RGB (R luminescentelement, G luminescent element, B luminescent element).

In such a cellular phone, a battery residual quantity picture whichshows residual quantity of a battery and an antenna picture which showsreception sensitivity are displayed on the upper part of the displayscreen of the color organic EL display 3114. In the present embodiment,the following three methods are proposed as the display method of suchspecific pictures.

The first method is a display method of a specific picture which isdisplayed on a color organic EL display 314 and a lighting part thereofincreases or decreases according to a situation, wherein the higher aprobability of lighting of a part, the lower luminance of the part isset beforehand.

The second method is a display method of a specific picture which isdisplayed at areas which overlie each other on a color organic ELdisplay 3114, in which two or three kinds of the specific picture inroughly classification are switched and displayed according to asituation, wherein a dot which constitutes each specific picture is setup in a manner where a color of an emitting element turned on differsmutually among the two or three kinds of the specific picture.

The third method is a display method of a plurality of specific pictureswhich is displayed on a color organic EL display 3114, wherein thehigher a frequency of displaying a pixel is, the lower luminance of thepixel is set beforehand.

Hereinafter, these method will be explained more concretely.

[1] Explanation About the First Method

[1-1] Explanation in the Case Where the First Method is Adopted to theBattery Residual Quantity Picture

As shown in FIGS. 14A-14E, a first picture showing a level of theresidual quantity of the battery with 0 to 3 bars (FIGS. 14A, 14B, 14C,14D), and a second picture showing a character of “charge” (FIG. 14E)are prepared for displaying the battery residual quantity picture. Thissecond picture is displayed when the residual quantity of the batterydecreases extremely.

The first picture consists of a battery frame figure imitated thebattery and bars displayed in the battery frame figure. As shown inFIGS. 14A, 14B, 14C, and 14D, the bars displayed in the battery framefigure change to four stages like 3, 2, 1, and 0. The more bars aredisplayed, the more residual quantity of the battery is left.

Five kinds of images shown in FIGS. 14A, 14B, 14C, 14D, and 14E areswitched and displayed according to the battery residual quantity level.The first picture (bar) is displayed in green for example, and thesecond picture (character of “charge”) is displayed in red.

In the first method, the higher a probability of lighting of a bar, thelower the luminance of the bar is set beforehand. The probability oflighting of the rightmost bar is highest, the probability of lighting ofthe leftmost bar is lowest, and the probability of the middle bar ismiddle of the rightmost bar and the leftmost bar. Therefore, the displayluminance of the rightmost bar 313 is set lowest, the display luminanceof the leftmost bar 311 is set highest, and the display luminance of themiddle bar 312 is set as the intermediate value thereof.

FIGS. 16A and 16B show a change over time of the display luminance ofthe rightmost bar which has high probability to light (solid line) and achange over time of the display luminance of the leftmost bar which haslow probability to light (doted line).

FIG. 16A shows a change over time of the display luminance in the casewhere the display luminance of the bar which has high probability tolight is set low beforehand (the first method). FIG. 16B shows a changeover time of the display luminance in the case where the displayluminance of the bars are set as equal value beforehand (theconventional method).

The reduction speed of the display luminance of the rightmost bar whichhas high probability of lighting is higher than that of the leftmost barwhich has low probability of lighting. Thereby, the difference betweenthe display luminance of these bars becomes gradually large whenaccumulated usage time of the cellular phone becomes long.

The display luminance of the leftmost bar and the display luminance ofthe rightmost bar are gradually averaged and the difference between thedisplay luminance of both becomes small as accumulative use time becomeslarge, because the display luminance of the bar which has higherprobability of frequency of lighting is set lower beforehand. If itpasses over the time when the difference between the display luminanceof both becomes zero, the difference of the luminance spreads to theopposite direction. Use time can be extended until the difference of theluminance becomes incapable for visibility.

Considering three bars, the display luminance of each bars are graduallyaveraged and the differences between the display luminance values ofeach bars become small as accumulative use time becomes large, becausethe display luminance of the bar which has higher probability offrequency of lighting is set lower beforehand in the first method. If itpasses over the time when the difference between the display luminanceof each bars becomes zero, the difference of the luminance spreads tothe opposite direction. Use time can be extended until the difference ofthe luminance becomes incapable for visibility.

[1-2] Explanation in the Case Where the First Method is Adopted to theAntenna Picture

As shown in FIGS. 17A-17E, a first picture showing a receivingsensitivity with 0 to 3 bars (FIGS. 17A, 17B, 17C, 17D), and a secondpicture showing a character of “outside” (FIG. 17E) are prepared fordisplaying the antenna picture. This second picture is displayed whenthe receiving sensitivity decreases extremely.

The first picture consists of a antenna figure imitated the antenna andbars displayed right side of the antenna figure. As shown in FIGS. 17A,17B, 17C, and 17D, the bars displayed right side of the antenna figurechange to four stages like 3, 2, 1, and 0. The more bars are displayed,the higher the receiving sensitivity of the antenna is.

Five pictures shown in FIGS. 17A-17E is switched and displayed accordingto receiving sensitivity. The first picture is displayed in green, thesecond picture is displayed in red, for example.

In the first method, the higher a probability of lighting of a bar, thelower the luminance of the bar is set beforehand. The probability oflighting of the leftmost bar is highest, the probability of lighting ofthe rightmost bar is lowest, and the probability of the middle bar ismiddle of the rightmost bar and the leftmost bar. Therefore, the displayluminance of the leftmost bar 321 is set lowest, the display luminanceof the rightmost bar 323 is set highest, and the display luminance ofthe middle bar 322 is set as the intermediate value thereof, as shown inFIG. 18.

Also in this case, the display luminance of each bars are graduallyaveraged and the differences between the display luminance values ofeach bars become small as accumulative use time becomes large, becausethe display luminance of the bar which has higher probability offrequency of lighting is set lower beforehand in the first method. If itpasses over the time when the difference between the display luminanceof each bars becomes zero, the difference of the luminance spreads tothe opposite direction. Use time can be extended until the difference ofthe luminance becomes incapable for visibility.

[2] Explanation About the Second Method

A display method of a specific picture which is displayed at areas whichoverlie each other on a color organic EL display, in which two or threekinds of the specific picture in roughly classification are switched anddisplayed according to a situation, wherein a dot which constitutes eachspecific picture is set up in a manner where a color of an emittingelement turned on differs mutually among the two or three kinds of thespecific picture.

As mentioned above, in the color organic EL display 3114, a single colorpixel is constituted with three kinds of organic EL elements (Rluminescent element, G luminescent element, B luminescent element) whichemit light in R, G, B, respectively. That is, the single color pixel isconstituted with three dots.

As the battery residual quantity picture, the first pictures showingresidual quantity level of the battery with 0-3 bar(s) (FIGS. 14A, 14B,14C, 14D) and the second picture showing the character of “charge” (FIG.14E) are switched and displayed according to the situation as mentionedabove.

In the second method, the dots which constitute the first picture (bar)and the second picture (character of charge) are set in a manner wherethe kind of color of the emitting elements turned on when displayingthese pictures differs each other.

FIG. 19A shows dots which constitute the picture (corresponding to thepicture shown in FIG. 14A) in which the lighting pixels are most amongthe first pictures. FIG. 19B shows dots which constitute the secondpicture (corresponding to the picture shown in FIG. 14E). FIG. 19C showsa relation between the position of the dots which constitute the firstpicture and the position of the dots which constitute the secondpicture.

In this example, the first picture is displayed only in green. All ofthe dots which constitute the first picture are G emitting elements. Onthe other hand, the second picture is displayed only in red. All of thedots which constitute the second picture are R emitting element.

The dots which constitute either the first picture or the second picturemay consist of the emitting elements of two colors (for example, Remitting element and G emitting element), and the dots which constituteanother picture may consist of a color different from above-mentionedtwo colors (for example, B emitting element).

In the second method, the dots which constitute the first picture andthe second picture are set in a manner where the kind of color of theemitting elements turned on when displaying these pictures differs eachother.

Therefore, the one picture is not influenced by the degradation of theluminance of another picture among the first picture and the secondpicture, even if these pictures are displayed almost the same area.

The second method can be also adopted to the first picture showing thereceiving sensitivity with 0-3 bar(s) (FIGS. 17A, 17B, 17C, 17D) and thesecond picture showing the character of “outside” (FIG. 17E) in theantenna picture.

[3] Explanation About the Third Method

FIG. 20 shows pictures which can be displayed on upper part of the colororganic EL display 3114.

In the third method, the higher a frequency of displaying the pictureis, the lower luminance of the picture is set beforehand among thesepictures 331-338.

Concretely, the picture 331 is a picture showing a state during atelephone call. The picture 331 is displayed only during the telephonecall. The display luminance of thereof is set high beforehand becausethe frequency of a display of the picture 331 is low.

The picture 332 is a picture showing residual quantity of the battery.The picture 332 is always displayed. The display luminance thereof isset low beforehand because the frequency of a display of the picture 332is high.

The picture 333 is a picture showing a state where a key of the cellularphone is locked. The picture 333 is only displayed when the key islocked. The display luminance thereof is set high beforehand because thefrequency of a display of the picture 333 is low.

The picture 334 is a picture showing a state where the cellular phone isin the manner mode. The picture 334 is only displayed when the cellularphone is in the manner mode. The display luminance thereof is set highbeforehand because the frequency of a display of the picture 334 is low.

The picture 335 is a picture showing a reception of a mail. The picture334 is only displayed when the mail is received. The display luminancethereof is set high beforehand because the frequency of a display of thepicture 335 is low.

The picture 336 is a picture showing a state where a search on the webis performed. The picture 336 is only displayed when the search on theweb is performed. The display luminance thereof is set high beforehandbecause the frequency of a display of the picture 336 is low.

The picture 337 is a picture showing the antenna. The picture 337 isalways displayed. The display luminance thereof is set low beforehandbecause the frequency of a display of the picture 337 is high.

The picture 338 is a picture showing a state where the cellular phone isin the character input mode. The picture 338 is only displayed when thecharacter is inputted. The display luminance thereof is set highbeforehand because the frequency of a display of the picture 338 is low.

That is, the display luminance of the pictures 332 and 337 which arefrequently displayed is set low among the pictures 331-338 in theexample shown in FIG. 20.

[Effect of the Third Embodiment]

According to the present embodiment, luminance degradation withdisplaying the specific picture can be made hard to be conspicuous.

FOURTH EMBODIMENT

[Field of the Fourth Embodiment]

The present embodiment relates to a display apparatus and a displaymethod, and it particularly relates to a technology for improving adisplay quality of the display apparatus and the display method.

[Related Art of the Fourth Embodiment]

Notebook type personal computers and mobile terminals are spreadingwidely. A liquid crystal display is mainly used as a display apparatusthereof. Organic EL (Electro Luminescence) display is expected as anext-generation flat display panel. As for the liquid crystal display,the straitness of the view angle and the lateness of response speedstill remain as a subject. On the other hand, the organic EL display cansolve the above-mentioned subject and can achieve high luminosity andhigh efficiency.

As for the organic EL display, however, it can not be avoided a changewith the passage of time, that is, degradation, of an optical elementbecause of the characteristic thereof. A white balance may collapse or avariation of luminance may be arisen by continuous use, even if thewhite balance is adjusted at the time of manufacture. It is known thatdegradation of the optical element of the organic EL display isremarkable compared with that of the liquid crystal display, and it isrecognized that it is a big problem in view of the quality of a product.

[Summary of the Fourth Embodiment]

The present embodiment has been made in view of the foregoingcircumstances and an object thereof is to improve reduction of displayquality caused by the above-mentioned variation of the luminance.Another object thereof is to avoid a phosphor burn-in of a display imagecaused by localizing the variation of the luminance.

An aspect of the present embodiment relates to a display apparatus. Thisapparatus is a display apparatus comprising: an optical element; aluminance information storing unit which stores luminance informationset to said optical element; and a display changing unit which changes adisplay image displayed on said display apparatus in a manner where aguessed value of degradation of each optical elements can be averagedbased on the luminance information stored.

Here, the display apparatus means an apparatus comprising a displayscreen, for example, a cellular phone, a PDA (Personal DigitalAssistant), a personal computer, and the like. An organic light emittingdiode (hereinafter, simply referred to as “OLED”) as an optical elementof an organic EL display deteriorates with passage of time as mentionedabove. Cause of the deterioration is considered a current supplied tothe OLED. The degradation of the OLED can be assumed by monitoring aluminance set to the OLED, for example, storing accumulated luminanceset to the OLED, since the luminance of light emitted from the OLED isdependent on the current. If the degradation of the OLED is averaged,the variation of the luminance can be avoided.

Generally, a specific character or a specific image is displayed on aspecific position in the display screen of the cellular phone in manycases. It may cause the phosphor burn-in. The degradation of the OLEDcan be averaged by changing a display position, luminance, or color toneof the character and the image displayed. Here, “average” may be a statealmost equalized, and equalization should just be the grade where a usercannot recognize the variation of the luminance.

In the case of color display in the organic EL display, the degradationspeed of the OLEDs of R (Red), G (Green), and B (Blue) differs since thematerials thereof differ each other. Thereby, there may be arisen aphenomenon that the display image is displayed in a little green forexample as the display is used. Therefore, it is necessary to equalizethe grade of degradation of the OLED of each color of R, G, and B.

Another aspect of the present embodiment also relates to a displayapparatus. This apparatus is a display apparatus comprising: an opticalelement; and a display changing unit which changes a display imagedisplayed on said display apparatus in a manner where a guessed value ofdegradation of each optical element can be averaged, maintaining anoutline of the display image.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; a display screen which is composed of aplurality of display areas; and a display changing unit which changes adisplay image of each display area, maintaining an identity of a contentof the display.

A display screen of the cellular phone, for example, may be divided intoa plurality of areas. A horizontally long and slender display area isset in the upper part of many cellular phones, and the picture whichshowing the residual quantity of a battery and the picture showing theintensity of an electric wave are displayed there. These pictures arealways displayed. Thereby, if the display area of these pictures isburned in, there arises a possibility that a user can not recognize theresidual quantity of the battery and the intensity of the electric wave.It is convenient that the picture displayed is changed for every dividedarea.

The display changing unit may change the display image again, when aguessed value of degradation of the optical element reaches apredetermined value from the last change as a starting point. Forexample, the display image may be changed when the accumulated value ofthe luminance set to the optical element exceeds a predetermined value,and the accumulated value of the luminance may be initialized in thecase where the change is performed. The display changing unit may changethe display image, when an absolute value of an accumulated differenceof a luminance of neighboring pixels exceeds a predetermined value.

That is, the difference between the degradation of optical elements ofneighboring pixels can be assumed by calculating the difference of theluminance thereof. The degradation of the pixel for a accumulating termcan be assumed by accumulating the difference over the term.

The display changing unit may change the display image, when adifference of a guessed value of degradation of the optical element in arow or a column of even number and odd number exceeds a predeterminedvalue. That is, The display image may be changed when a differencebetween the accumulated luminance set to the even-numbered row and theaccumulated luminance set to the odd-numbered row, or a differencebetween the accumulated luminance set to the even-numbered column andthe accumulated luminance set to the odd-numbered column exceeds apredetermined value.

The display image may be changed when following two conditions arefulfilled. First, the difference of the luminance set to theeven-numbered and odd-numbered rows or columns in the image previouslydisplayed is accumulated. The difference of the luminance set to theeven-numbered and odd-numbered rows or columns in the image to bedisplayed next is accumulated. Then, the display image may be changed sothat the degradation of the optical element can be averaged according towhether each accumulated value is positive or negative. Moreover, theluminance set to the even-numbered and odd-numbered rows or columns inthe image previously displayed is accumulated. The luminance set to theeven-numbered and odd-numbered rows or columns in the image to bedisplayed next is accumulated. Then, the display image may be changed sothat the degradation of the optical element can be averaged according towhich of the accumulated values is greater. In the case of these twoconditions, it is not necessary to prepare a memory storing apredetermined value which is a threshold value at the time of changingthe display image in a circuit.

The display changing unit may change, when a power supply of the displayapparatus is turned on or off, the display image in the process ofturning the power on or off. For example, a user may not be noticed thechange of the display image by changing the display image when the userdoes not see the display apparatus. The display changing unit maychange, when an application displayed on the display apparatus ischanged, the display image in the process of the change of theapplication.

The display screen of the display apparatus can be opened and closed,the display apparatus may further comprise an opening-and-closingdetecting unit which detects opening or closing of the display screen;and the display changing unit may change the display screen when openingand closing of the display screen are detected by theopening-and-closing detecting unit. An operating unit for operating thedisplay apparatus may be slide-type; the display apparatus may furthercomprise a slide detecting unit which detects a slide of the operatingunit; and the display changing unit may change the display screen whenthe slide of the operating unit is detected by the slide detecting unit.For example, in the case where the operating unit like a keyboard isnormally hidden under the display screen and is slid out when operatingin the cellular phone, the display screen may be changed by operation ofsliding out or closing of the operating unit.

The display changing unit may change the display image by shifting adisplay position of the display image. The display changing unit mayadjust a signal set up to each optical element according to a guessedvalue of degradation of the optical element. For example, thedegradation grade of the optical element may be assumed by accumulatingthe luminance set to the optical element as mentioned above. Theluminance set to the optical element whose degradation is assumed largemay be adjusted so that the variation of the luminance can be avoidedbased on the thus assumed value of degradation.

The display changing unit may include an area detecting unit whichdetects a specific area, the display position thereof is to be shifted,among an area of the display image; and the display changing unit maychange the display image by shifting the display position of thespecific area detected. The display image can be relatively easilychanged if the size and the display position is managed by an MPU or amemory comprised by the display apparatus. On the other hand, although adisplay screen appears to be divided into plurality, the display screendisplayed on each may not be managed individually, but may besubstantially managed as one display screen inside the displayapparatus. Even in such a case, only a certain image displayed on thecertain divided display screen may be shifted.

For example, a display screen of a cellular phone is exemplified. Thedisplay screen of the cellular phone comprises elongated display areasin top and bottom, and relatively large display area in middle. In thetop and bottom area, an image showing a state of an electric wave and animage showing residual quantity of a battery are displayed for example.In the middle area, an electric mail is displayed, or a background imageis displayed when the cellular phone is not used.

Only the background image displayed in the middle display area may beshifted since there is a possibility of phosphor burn-in if the sameimage is always displayed. When three areas are managed as one displayscreen, only the image displayed in the middle needs to be taken out andshifted. When the image is constituted by the background image of asingle color and an image such as an illustration in it, Only theillustration is taken out and shifted.

The display changing unit may determine an amount of compensation to begiven to a signal according to a value of the signal, when adjusting thesignal set up to said optical element. For example, if the same amountof compensation is given to the signal in the case where the lowluminance is set to the optical element and in the case where the highluminance is set to the optical element, there is a possibility that theinfluence given to the display image in the case where the low luminanceis set is larger. Thereby, a processing of reducing the amount ofcompensation given to the signal is performed when the low luminance isset.

The display changing unit may determine an amount of compensation to begiven to a signal based on the guessed value of degradation of theoptical element of a surrounding pixel, when adjusting the signal set upto the optical element.

The display changing unit may change the display image by changing adisplay color of each optical element. The display changing unit maychange the display color for a predetermined cycle. As mentioned above,when the accumulated luminance is reached to a predetermined value, andthere is not an input from a user for a predetermined term, in a casewhere the accumulated value of luminance of green is small for example,the whole display image may be changed to green. The change of thedisplay color may be made by changing gradually a luminance ratio of theoptical element corresponding to each color which constitutes a pixel.

A display area needed for displaying an actual display image may be setup smaller than an effective display area which can be displayed in saiddisplay apparatus; and the display changing unit may shift the displayarea in the effective display area. For example, in the case where thedisplay screen is constituted by 105*105 pixels, the display area to beactually displayed may be 100*100 pixels, and five pixels of verticaland horizontal direction may be an area in which the image can beshifted.

The optical element may correspond to a dot, a pixel may include dots ofa plurality of colors, and the display changing unit may shift thedisplay image per dot, and may change combination of the opticalelements which originally constitute one pixel. As mentioned above, onepixel of the color display apparatus is generally constituted by dots ofthree colors of R, G, and B. Thereby, the display image may be shiftedper pixel or per dot.

In a case where the display image to be shifted includes a character,the display changing unit may set a margin space which is originally setfor displaying the character not to touch each other as an area in whichthe arbitrary character can be shifted. Generally, the font does not useone line in one side of the display area so that the font may notcontact with a neighbor font, and the line is set as the margin area. Ina case of the font of 16*16 pixels, for example, only. 15*15 pixels areused actually. Thereby, each vertical and horizontal one line can beused as the display area of the font.

In a case where the display image to be shifted includes a character,the display changing unit may shift the display image to a direction inwhich influence for readability of the character is small when a usersees the character. For example, the display changing unit may scrollthe character string horizontally when the user sees an e-mail on thedisplay screen of the cellular phone.

The display changing unit may scroll the display image or may perform amosaic processing to the display image and displays it when there is noinput from a user for predetermined period. A size of a block generatedby the mosaic processing may be changed with passage of time.

The display changing unit may select, when a background image whichfunctions as a wallpaper is newly set up, the wallpaper according tograde of degradation of said optical element. Here, “set the wallpaper”means both of a case where a new wallpaper is selected as the backgroundimage, and a case where a color of the displayed wallpaper is changedand set as the background image.

The reduction of the luminance of each color can be averaged by changingthe color of the wallpaper according to the grade of the assumeddegradation of the optical element. Moreover, in a case where thereduction of the luminance of red is assumed large, the reduction of theluminance of each color can be averaged by setting an image in whichgreen and blue is largely used as the wallpaper.

The color tone of the wallpaper may be changed by adjusting the whitebalance of the selected wallpaper so that the degradation of the opticalelement corresponding to each color of RGB can be averaged. Since theadvance degrees of degradation of the OLED of each color differ in theorganic EL display especially, such a setup is highly effective.

Another aspect of the present embodiment relates to a display method.This method is a display method in a display apparatus which comprisesan optical element, the method including: storing information ofluminance set up to the optical element; and changing a display imagedisplayed on the display apparatus in a manner where a guessed value ofdegradation of each optical element can be averaged based on theluminance information stored.

Further another aspect of the present embodiment also relates to adisplay method. This method is a display method in a display apparatuswhich comprises an optical element, the method including: changing adisplay image displayed on the display apparatus in a manner where aguessed value of degradation of each optical element can be averaged,maintaining an outline of the display image.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses andsystems may also be practiced as additional aspects of the presentinvention.

[Example of the Third Embodiment]

Premise Technology

In advance of explanation of the present embodiment, a structure of anorganic EL display as the premise technology of the present embodimentis explained. FIG. 21 is a block diagram showing a basic structure of anorganic EL display apparatus 410. The organic EL display apparatus 410is constituted by an image source input unit 420, an organic EL drivingcircuit 430, and an organic EL panel 460.

The organic EL driving circuit 430 comprises an image adjusting unit 432which carries out various processings to a digital image signal inputtedfrom the image source input unit 420, an MPU (Micro Processing Unit) 434which calculates when these processings are carried out, and a DAC(Digital to Analog Converter) unit 442 which converts the image signalcarried out processing to an analog signal. The organic EL drivingcircuit 430 further comprises a control signal generating unit whichgenerates various timing control signals and a memory which functions atable when actual processing is carried out, which are not shown in thefigure.

The image adjusting unit 432 performs an offset adjusting to adjust abrightness, a gain adjusting to adjust a contrast, and a processing toadjust input image signal which is performed gamma correction tovoltage-emitting luminance (V-T) characteristic of the organic EL panel.

Operation by the above structure is explained briefly. Three kinds ofthe digital signals R_in, G_in, and B_in are inputted from the imagesource input unit 420 to the image adjusting unit 432. The imageadjusting unit 432 performs image adjusting processing like the offsetadjusting and the gain adjusting. The digital signals are outputted fromthe DAC unit 442 as three kinds of analog signals R_out, G_out, andB_out to the organic EL panel 460.

In terms of hardware, this structure can be realized by a CPU, a memoryand other LSIs of an arbitrary computer. In terms of software, it isrealized by memory-loaded programs or the like, but drawn and describedhere are functional blocks that are realized in cooperation with those.Thus, it is understood by the skilled in the art that these functionalblocks can be realized in a variety of forms by hardware only, softwareonly or the combination thereof.

FIRST EXAMPLE

In a first example, luminance set to an OLED constituting each dot of adisplay screen is monitored. When an accumulated value thereof reaches apredetermined condition, a part or the whole of a display image isshifted. The degradation of the OLED is averaged by averaging theluminance set to the OLED corresponding to each dot.

A condition of the accumulated value for shifting the display image maybe, for example, (1) when the accumulated value of the luminance in apredetermined term exceeds a predetermined value, (2) when the absolutevalue of the accumulated value of a difference between the luminance ofneighboring pixels exceeds a predetermined value, (3) when a differencebetween the accumulated value of the luminance of an even-numberedcolumn and that of an odd-numbered column exceeds a predetermined value.

FIG. 22 shows a state where a character “0” is displayed on a displayarea of 9×8 pixels, and it is shifted one pixel to the right and downdirection respectively. A character shown by black painting is acharacter before being shifted, and a character shown with slash is acharacter after being shifted.

FIGS. 23A, 23B, and 23C show an example in which a display image shiftedper 1 dot. FIG. 23A shows an initial state before being shifted, FIG.23B shows a state where the display image is shifted one dot to rightdirection, and FIG. 23C shows a state where the display image is shifted2 dots to right direction. In the initial state, combination of colorsof the dots which constitute a pixel is R, G, B in order from the left.In the state where the display image is shifted one dot to rightdirection, for example, the combination is G, B, R in order from theleft.

FIG. 24 shows a state where the display area A2 which is actuallydisplayed is set up smaller than an effective display area Al which candisplay the display picture. For example, when the display area A2consists of 100×100 pixels, the effective display area Al consists of105×105 pixels. The display area A2 has an area in which the displayimage can be shifted 5 pixels in the length and the transverse directioneach.

FIG. 25 shows a state where a Japanese character is displayed on an areaof 8×8 pixels. Pixels of the top line and the rightmost column are setup as a blank space area so that the character may not be touched withan adjoining character. This area is also used as a display area at thetime of shifting a character. When the character sequence consists oftwo or more characters, a character may shift 1 pixel to up, or 1 pixelto right, or not shift at all, for example. Thereby, phosphor burn-incan be reduced without spoiling display grace greatly.

The above-mentioned shift of the display image may be carried out with apredetermined cycle. The shift can be performed without making a userconscious of the shift by shifting the display image when the user doesnot operate the display apparatus or the display screen is changedconsiderably.

The timing of shifting may be, for example, (1) when the power of thedisplay apparatus turns on or off, (2) when the display apparatus isopened or closed in a case where the display apparatus can be opened andclosed like a fold-down type cellular phone, (3) when changing anapplication, (4) when there is no operation from a user for apredetermined term, (5) when an operating unit is slid out or closed ina case where the operating unit of the cellular phone is a slide typeand can be opened and closed.

FIG. 26 shows a structure of an organic EL display apparatus 4100according to the present example. The basic structure is the same as thestructure shown in FIG. 21 in the premise technology. Particularlycharacteristic structure in the present example will be explained.

An organic EL driving circuit 430 includes a luminance accumulating unit452 which acquires and stores luminance set to the OLED, a look-up table343 which stores an above-mentioned condition about the accumulatedluminance when shifting the display image and how to shift the displayimage, and a shift condition table 456 which stores above-mentionedtiming of shifting. An image adjusting unit 432 includes an imageshifting unit 450 which carries out processings for shifting anddisplaying the display image. The organic EL apparatus 4100 includes amode switch detecting unit 470 which detects a timing of shifting thedisplay image.

The luminance accumulating unit 452 accumulates the luminance set toeach OLED which constitutes each pixel and stores thus accumulatedluminance. The image source input unit 420 includes an image changingunit 458 which carries out a mosaic processing and color change of thedisplay image shown in examples 2-4 with reference to the accumulatedluminance stored in the accumulated luminance storing unit 452.

Operation about the shift of the display image by the above structure isexplained briefly. The mode detecting unit 470 detects the timing ofshifting the display image, for example, when the application is changedand the like, and transmits the timing to the organic EL driving circuit430. The MPU 434 refers to the shift condition table 456. If it is thetiming to shift, the MPU 434 further refers to the look-up table 454based on the accumulated luminance stored in the accumulated luminancestoring unit 452. If the accumulated luminance is in the predeterminedcondition, the MPU 434 instructs to shift the display image to the imageshifting unit 450.

According to the first example, the degradation of specific OLED can beavoided and the phosphor burn-in of the display screen can be avoided byshifting the display image in accordance with the accumulated value ofthe luminance set to the OLED. Moreover, the degradation of the OLED inthe whole display screen can be averaged and the variation of theluminance can be reduced.

SECOND EXAMPLE

In the first example, the display image is shifted per dot or per pixelunder a predetermined condition. In the second example, when apredetermined time has passed after a user operation is completed, apart of the displayed image is scrolled horizontally or vertically, oris carried out a mosaic processing.

FIG. 27A shows an initial display image, in which a white circle and ablack triangle are displayed. FIG. 27B shows a state where images of thecircle and the triangle are scrolled horizontally. FIG. 27C shows astate where images of the circle and the triangle are scrolledvertically.

For example, the degradation of the OLED is nearly equal in an area A3where the image of the circle shown in FIG. 27B is scrolled. The averageluminance in the whole display screen can be equaled by combination ofthe scroll to the horizontal direction and the scroll to the verticaldirection.

FIGS. 28A and 28B show a state where the display image is carried out amosaic processing. This processing is also carried out when apredetermined time has passed after completed the user operation. FIG.28A shows a display image at an initial state. FIG. 28B shows a displayimage carried out the mosaic processing. The phosphor burn-in of thedisplay screen can be further reduced by changing a size of a blockgenerated by the mosaic processing with progress of time.

The above-mentioned scroll processing and mosaic processing can beachieved by the structure of the apparatus shown in FIG. 25 in the firstexample. According to the second example, the same effect as the firstexample can be acquired.

THIRD EXAMPLE

In the first example and the second example, the degradation of the OLEDis averaged and the phosphor burn-in is reduced by shifting the displayimage. In the third example, the degradation grade of the OLED emittinglight of each color of R, G, and B is averaged by adjusting a signal setto the OLED corresponding to each dot and adjusting a color of thedisplay image.

In the case of adjusting the color, the color may be adjusted onlypaying attention to a single pixel. The display image may be dividedinto blocks, 3*3 pixels for example, and the color may be adjusted sothat balance in the block may be maintained. The blocks may be changedwith progress of time.

In the case where the color tone of the adjusted image is changedremarkably from the display image before adjusted, the amount ofadjusting may be adjusted to make the color tone not change a lot. Forexample, when the luminance ratio of R, G, and B is 50% in whiterespectively, the adjusting may be made where the luminance ratio or Ris made into 49%, and the luminance ratio of G and B are made into 51%,for example.

FIGS. 29A and 29B are schematic figures showing a state where a displaycolor is changed at a fixed timing to average the emitting luminance ofeach color of RGB over time. The upper column shows an emitting colorand the lower column shows amplitude of a signal. This change may bemade per dot or may be performed to the whole display screen.

FIG. 29A shows a state where only R is displayed among three colors ofRGB. The amplitude of the signal set to the OLED is 0 except R. When apredetermined time has passed after this state, only G is emitted asshown in FIG. 29B for example. Here, RGB is emitted individually, butmixed colors may be emitted.

Moreover, when changing the emitting color, the luminance ratio of RGBmay be gradually changed as shown in FIGS. 30A-30C. At first, only R isemitting light as shown in FIG. 30A, then the signal amplitude of Rbecomes small and G emits light as shown in FIG. 30B. Furthermore, withprogress of time, three colors of RGB emit light with the same signalamplitude as shown in FIG. 30C.

Above-mentioned processing can be realized with the structure shown inFIG. 26 of the first example. However, in this example, since a displayimage is not shifted, the image shifting unit 450 is unnecessary.

FIG. 31 is a flowchart showing a procedure of a processing of theabove-mentioned color change. After a predetermined time has passed fromend of the user operation (Y of S410), when the mode is changed (Y ofS412), the accumulated value of the luminance set to the OLEDconstituting the display screen is acquired (S414). In the case wherethe mode is not changed (N of S412), the procedure is returned to theprocessing of S410.

In the case where the degradation of the OLED corresponding to RGB istaken into consideration (Y of S416), the accumulated value ismultiplied by a predetermined degradation rate and corrected (S418). Inthe case where the degradation rate is not taken into consideration (Nof S416) and after correction in S418, the accumulated value of theluminance is inverted (S420). The signal for averaging the accumulatedvalue in the display screen is outputted (S422). It subtracts from theinverted accumulated value according to the luminance set (S424) and theaccumulated value of the luminance is updated (S426). If the updatedaccumulated value is averaged in the display screen (Y of S428), thiscolor change processing is completed. If not averaged (N of S428), thesteps S414 to S426 is repeated.

In S420 and S424, the accumulated value is inverted and subtracted theset luminance, but the processing may not be restricted to this, theprocessing may be made as the maximum of the accumulated value iscalculated, and the set-up luminance is added to average the accumulatedvalue.

FIG. 32 is a flowchart showing a procedure of adjusting the displayimage according to the accumulated value of the luminance set to theOLED. The accumulated value of the luminance is acquired (S450). In thecase where the degradation of the OLED corresponding to RGB is takeninto consideration (Y of S452), the accumulated value is multiplied by apredetermined degradation rate and corrected (S454).

In the case where the degradation rate is not taken into consideration(N of S452) and after correction in S454, it is checked whether theaccumulated value of the luminance is averaged in the display screen. Ifaveraged (Y of S456), the inputted signal is outputted as it is (S462).If not averaged (N of S456), the gain of the luminance set to each OLEDis adjusted not to arise the variation of the luminance (S458), and thusadjusted signal is outputted (S460).

After the signal is outputted in S460 or S462, the accumulated value isupdated reflecting the luminance set (S464). If the adjusting iscontinued (Y of S466), the steps S450 to S464 are repeated. If theadjusting is not continued (N of S466), the processing is ended.

When adjusting the signal in S458, the gain is adjusted bymultiplication of the signal, but the processing may not be restrictedto this, the processing may be made by addition or subtraction of thesignal. As mentioned above, according to the third example, the sameeffect as the first example and the second example is acquired, and theadjust of the display image in consideration of the variation of theluminance can be carried out.

FOURTH EXAMPLE

In this example, when the background image which functions as awallpaper is newly set up, color tone of the wallpaper is changedaccording to the grade of degradation of the OLED of each dot of adisplay screen. This change of the color tone may be made for vanishingthe variation of the luminance caused by the degradation the OLED, orfor averaging the grade of degradation of the OLED. For example, when itis presumed that the grade of degradation of the OLED of R is large onthe whole display screen, the wallpaper is set up with the ratio ofother G or the color of B being enlarged.

The apparatus to realize this example can be realized with the structureshown in FIG. 26 of the first example. As mentioned above, according tothe fourth example, the same effect as the third example is acquired.

FIFTH EXAMPLE

In the present example, display screen of the cellular phone is dividedinto three areas of upper, middle, and lower, and the display image isshifted in each divided area independently. FIG. 33 is a figure showingthe display screen of the cellular phone. The display screen is dividedinto three areas of the first area L1, the second area L2, and the thirdarea L3, in order from the top.

In the first area L1, a battery mark DM which is a picture showingresidual quantity of the battery is displayed in left side, and anantenna mark AM which is a picture showing intensity of an electric waveis displayed in right side. The battery mark DM and the antenna mark AMare always displayed at a fixed position in many cellular phones. Thereis a probability of phosphor burn-in of these pictures. If the phosphorburn-in with a shape of the battery mark DM is arisen, there arises aprobability that residual quantity of the battery cannot be shownproperly to a user. Thereby, the battery mark DM and the antenna mark AMare shifted in only the first area L1. Since the first area L1 ishorizontally long, horizontal scrolling, horizontal swing and the likeare illustrated as the method of shifting the battery mark DM and theantenna mark AM. The horizontal scroll means shifting the battery markDM and the antenna mark AM along a fixed direction. The horizontal swingmeans shifting the antenna mark DM and the antenna mark AM right andleft by arbitrary number of pixels. That is, in the horizontal swing,the battery mark DM and the antenna mark AM is displayed swingingly.

The visibility does not get worse so much by shifting the battery markDM and the antenna mark AM only horizontally because the displayposition thereof can be roughly predicted. Similarly, the picturedisplayed on the third area L3 is also shifted in the third area L3maintaining visibility. The picture of a car displayed on the secondarea L2 (hereinafter simply referred to as a “car picture”) TM may bescrolled arbitrary direction horizontally and vertically since the carpicture is a background picture here, and the visibility thereof is notrequired from the user. The car picture TM displayed on the second areaL2 in the middle once moves downward, then moves to down and rightdirection.

FIG. 34 shows a state where the image displayed on the display screenshown in FIG. 33 is shifted. The battery mark DM and the antenna mark AMare scrolled right and left respectively. All the pictures displayed onthe third area L3 are scrolled right. The car picture TM displayed onthe second area L2 in middle is once shifted below, and shifted to rightbottom after that.

A structure of the cellular phone for shifting the display image forevery divided area. FIG. 35 is a figure showing the structure of thecellular phone 4200 according to the present example. The cellular phone4200 comprises an MPU 434, a graphics memory 474, a timing control IC(Integrated Circuit) 476, a flash memory 472 and an organic EL panel460. The cellular phone 4200 further comprises a speaker 462, atransmitter-receiver unit 464, and a microphone 466.

The flash memory 472 stores data to be held when the power of thecellular phone 4200 is off. The graphics memory stores image datadisplayed on the organic EL panel 460. The image data is written in thegraphics memory 474 when receiving the image data and a write positioncontrol of the image data from the MPU 434. The graphics memory 474outputs the image in response to an input of a read control signalsynchronized with the display from the timing control IC 476.

The timing control IC 476 supplies the read control signal to thegraphics memory 474 synchronizing with a scan timing of the organic ELpanel 460 and reads the image data from the graphics memory 474. Thetiming control IC 476 supplies the thus read image data and a drivingsignal to the organic EL panel 460 and displays the display image on theorganic EL panel 460. The timing control IC 476 also detects avertically start point VS, a vertically end point VE, a horizontallystart point HS, and a horizontally end point HE of the car picture TMdisplayed on the second area L2 shown in FIG. 33.

FIG. 36 is a figure showing relation between the display image displayedon the organic EL panel 460 and not scrolled and the memory space. Thedisplay area of the organic EL panel 460 is constituted by 199*99pixels. A left top position of this image corresponds to an address (0,0) in the memory space and a right bottom position thereof correspondsto an address (199, 99).

The image data is written at the address in which the display imagecorresponds one by one to the memory space in the graphics memory 474 bythe MPU 434 as shown in FIG. 36. The scroll of the image in the organicEL panel 460 is performed by changing a timing of reading the image databy the timing control IC 476. The method of scrolling in the first areaL1, the method of scrolling in the second area L2, and the method ofscrolling in the third area L3 differ each other. The method ofscrolling in the first area L1 and in the third area L3 may be the same.

Reading the image data by the timing control IC 476 is explained basedon FIGS. 37A and 37B. Upper column shows the memory space and lowercolumn shows the display image. FIG. 37A shows a procedure of readingthe image data written in the memory space in the case without scroll.The image data written in the memory space is the same in FIG. 37A andin FIG. 37B.

The read of the image data without scroll is carried out toward ahorizontal direction one by one from the address (0, 0) S1 to theaddress (0, 99). Then, moving to the bottom of one line and the imagedata at the address (1, 0) is read. Similarly, the image data issequentially read until the address (199, 99).

On the other hand, the read of the image data with scroll is shown inFIG. 37B. In this figure, the display image is scrolled onlyhorizontally in the first area L1 and in the third area L3. The displayimage is shifted 50 pixels rightward. In the second area L2, the displayimage is scrolled not only horizontally but vertically.

The read of the image data is started at the address (0, 50). The imagedata is read sequentially. When the image data at the address (0, 99) isread, moving back to the top of the line, image data from the address(0, 0) to the address (0, 49) is read. Then, image data at the address(1, 50) in a lower row is read. Similarly, the image data in the row issequentially read.

Next, read of the image data in the first area L1 is completed, thenread of the image data in the second area L2 is started. In the secondarea L2, the car picture TM is displayed from the left top point GS. Theimage data is read from the address corresponding to the point GS. Thisaddress is referred to as the image start address M1 for conveniencesake. The image data is read from the address M1. If the image data isread to the bottom row of the second area L2, the image data in the toprow of the second area L2 is read. If the image data is read to theaddress just before the address M1, all of the image data in the secondarea L2 is read.

Then, the image data in the third area L3 is started. Similar to thedisplay image in the first area L1, the display image in the third areaL3 is shifted 50 pixels leftward. Therefore, read-out is started fromthe image data at the address moved horizontally 50. Read of the imagedata in the third area L3 is carried out like read of the image data inthe first area L1.

If the size and the display position of the display image are known whenscrolling in the second area L2, it is possible to display the displayimage so that the display image may not be protruded from the organic ELpanel 460. Since the MPU 434 is writing the image data in the graphicsmemory 474, the address of the start position GS of the image and theaddress of the end position GE of the image are grasped by the MPU 434.For this reason, the MPU 434 sets the read-out start address in thesecond area L2 so that the image may not be protruded from the organicEL panel 460. The scroll of the display image can be achieved bychanging the address over time.

On the other hand, if the MPU 434 does not manage the size and thedisplay position of the display image, the timing control IC 476 managesthe size and the display position of the display image by detecting theimage start position GS and the image end position GE of the displayimage.

The MPU 434 writes the only required image data which is corrected fromthe last display image to the graphics memory 474 one after another.Thereby, the MPU 434 may be unable to manage the picture start positionGS and the picture end position GE in the second area L2. However, whenthe timing control IC 476 reads the image data from the memory, thepicture start position GS and the picture end position GE of the secondarea L2 can be detected. The MPU 434 can manage the display position ofthe image by notifying the detected picture start position GS and thepicture end position GE to the MPU 434. Scrolling without a protrusionof the image can be realized by setting the read-out start address ofthe second area L2 to the timing control IC 476.

The procedure of detecting the picture start position GS of the 2nddomain L2 by the timing control IC 476 and the picture end position GEis explained. It is assumed that a non-image area is covered with asingle color as a premise. The address space of the second area L2 isknown. If the data of the color which is not a non-image is outputted tothe image data of the address in the second area L2, the timing controlIC 476 detects the minimum address and the maximum address in horizontaland vertical for every frame. The detected addresses may be the picturestart position GS and the picture end position GE in the second area L2.Here, the non-image area means the area other than the car picture TMamong the second area L2.

As mentioned above, according to the fifth example, generating ofphosphor burn-in can be reduced by shifting independently the imagedisplayed on the display screen of the cellular phone according to thedivided area, without getting worse a user's visibility.

These embodiments have been given solely by way of illustration. It willbe understood by those skilled in the art that various modifications maybe made to combinations of the foregoing components and processes, andall such modifications are also intended to fall within the scope of thepresent invention. Such modifications are given below.

In this embodiment, the image shifting unit 450 which shifts a displayimage is comprised in the image adjusting unit 432, the image shiftingunit 450 may be comprised in the image source input unit 420 and thedisplay image inputted in the organic EL driving circuit may be changed.

In this embodiment, the above-mentioned three conditions of theaccumulated value of luminance at the time of shifting the display imageare exemplified, but not restricted with these. For example, thedifference of luminance set to the optical elements in the odd-numberedcolumns and the even-numbered columns may be accumulated until a certaintime. And the difference of luminance set to the OLEDs in theodd-numbered columns and the even-numbered columns in the image to bedisplayed next may be accumulated. Then, the display image may bechanged so that the degradation of the OLED may be averaged according towhether the accumulated value is positive or negative. The luminance setto the OLEDs in the odd-numbered columns and the even-numbered columnsmay be accumulated until a certain time. And the luminance set to theOLEDs in the odd-numbered columns and the even-numbered columns in theimage to be displayed next may be accumulated. Then, the display imagemay be changed so that the degradation of the OLED may be averagedaccording to which of the accumulated value is greater. Here, theluminance set to the OLEDs in the even-numbered columns and theodd-numbered columns is compared, but the luminance set to the OLEDs inthe even-numbered lines and the odd-numbered lines may be compared.

[Effect of the Fourth Embodiment]

The deterioration of display quality of the display apparatus can besuppressed according to the present embodiment. Particularly, thevariation of the luminance in one screen and the deviation of the whitebalance can be mended. Moreover, the phosphor burn-in of a screen can beprevented in another viewpoint.

FIFTH EMBODIMENT

[Field of the Fifth Embodiment]

The present embodiment relates to a display apparatus, and itparticularly relates to a technology for improving a display quality ofthe display apparatus.

[Related Art of the Fifth Embodiment]

Notebook type personal computers and mobile terminals are spreadingwidely. A liquid crystal display is mainly used as a display apparatusthereof. Organic EL (Electro Luminescence) display is expected as anext-generation flat display panel. As for the liquid crystal display,the straitness of the view angle and the lateness of response speedstill remain as a subject. On the other hand, the organic EL display cansolve the above-mentioned subject and can achieve high luminosity andhigh efficiency.

As for the organic EL display, however, it can not be avoided a changewith the passage of time, that is, degradation, of an optical elementbecause of the characteristic thereof. A white balance may collapse or avariation of luminance may be arisen by continuous use, even if thewhite balance is adjusted at the time of manufacture. It is known thatdegradation of the optical element of the organic EL display isremarkable compared with that of the liquid crystal display, and it isrecognized that it is a big problem in view of the quality of a product.

In the organic EL display comprised in a cellular phone especially, aspecific character or a specific character string is continuouslydisplayed on a specific place in many cases. Hereafter, both of acharacter and a character string are also referred to as a “characterstring.” Generally, in consideration of a user's visibility, such acharacter string is set up so that it can be clearly distinguished fromthe color of the circumferences, such as a background picture.Therefore, a remarkable difference of advance of degradation between theoptical elements of an area in which the character is displayed and thesurrounding optical elements tends to appear.

Moreover, since a character string is displayed from the upper part of adisplay screen when the character string contained in texts such as anE-mail is displayed, advance of degradation of an optical elementdiffers in the upper part and a lower part of a display screen. Thevariation of luminance may be arisen thereby.

[Summary of the Fifth Embodiment]

An object of the present embodiment is to improve reduction of displayquality caused by the above-mentioned variation of the luminance.Another object of the present embodiment is to avoid a phosphor burn-inof a display image caused by localizing the variation of the luminance.

An aspect of the present embodiment relates to a display apparatus. Thisdisplay apparatus is a display apparatus comprising: an optical element;and a display changing unit which changes display form of a text datadisplayed on said display apparatus in a manner where a guessed value ofdegradation of each optical element can be averaged; wherein saiddisplay changing unit changes, when a power supply of said displayapparatus is turned on or off, the display form of the text data in aprocess of turning the power on or off. Here, the text data means acharacter.

Here, the display apparatus means an apparatus comprising a displayscreen, for example, a cellular phone, a PDA (Personal DigitalAssistant), a personal computer, and the like. An organic light emittingdiode (hereinafter, simply referred to as “OLED”) as an optical elementof an organic EL display deteriorates with passage of time as mentionedabove. Cause of the deterioration is considered a current supplied tothe OLED.

As mentioned above, a specific character or a specific image isdisplayed on a specific position in the display screen of the cellularphone in many cases. It may cause the phosphor burn-in. The degradationof the OLED can be averaged by changing a display position, luminance,or color tone of the character and the image displayed. Here, “average”may be a state almost equalized, and equalization should just be thegrade where a user cannot recognize the variation of the luminance.

In the case of color display in the organic EL display, the degradationspeed of the OLEDs of R (Red), G (Green), and B (Blue) differs since thematerials thereof differ each other. Thereby, there may be arisen aphenomenon that the display image is displayed in a little green forexample as the display is used. Therefore, it is necessary to equalizethe grade of degradation of the OLED of each color of R, G, and B.

The change can be performed without making a user conscious by changingthe display form of the text data when the user does not use the displayapparatus. The form of the text data may be a kind, a size, a color, abrightness of the font for example. A color or a brightness of thebackground of the text data displayed may be changed.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes, when anapplication displayed on said display apparatus is changed, the displayform of the text data in a process of the change of the application. Thechange of the application may be a change an application displayed on adisplay screen of a cellular phone from a web browser to an e-mailapplication for example. Moreover, it is contained in the change of theapplication, in a case where the frame which displays a certainapplication is changed to another frame, even if the application isperformed and displayed. For example, in the case where the web browseris displayed, for example, the change of the frame which displayscontents such as a homepage is included in the change of theapplication. Moreover, in the case where E-mail software is displayed,for example, the change from the screen for selecting the E-mailreceived to the screen which displays the E-mail actually selected isincluded in the change of the application.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes, when anelectric mail is displayed on said display apparatus, the display formof the text data for every electric mail. That is, the display form ofthe text data is changed according to the electric mail displayed whenreceived electric mail is displayed or when the electric mail undercreation or edit is displayed.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising an optical element, a display screen thereof can be openedand closed, the display apparatus comprising: a display changing unitwhich changes display form of a text data displayed on said displayapparatus in a manner where a guessed value of degradation of eachoptical element can be averaged; and an opening-and-closing detectingunit which detects opening or closing of the display screen; whereinsaid display changing unit changes the display form of the text datawhen opening and closing of the display screen are detected by saidopening-and-closing detecting unit.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes, while acharacter input means comprised in said display apparatus is operatedfor input of the character, the display form of the text data. Thechange of the display form of the text data is not limited to the changementioned above, the color and the background color of the font may bereversed. The brightness of these colors may be adjusted according tothe guessed value of the degradation of the optical element at the timeof the reverse.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes, when anelectric mail is displayed, the display form of the text data to bedisplayed according to whether the electric mail has already been reador has not been read yet. For example, a kind or size of a font of theelectric mail which is already read or is not read yet when displayingthe electric mail received.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes the displayform of the text data according to the size of the text data to bedisplayed when an electric mail is displayed. For example, the size ofthe font is set large in the case where the size of the text data is 10characters, the size of the font is set small in the case where the sizeof the text data is 100 characters.

The display changing unit may change the display form of the text databy changing a font type of the text data.

The display changing unit may shift an arbitrary character included inthe text data using a margin space which is originally set to avoiddisplaying the characters touching each other.

Generally, the font does not use one line in one side of the displayarea so that the font may not contact with a neighbor font, and the lineis set as the margin area. In a case of the font of 8*8 pixels, forexample, only 7*7 pixels are used actually. Thereby, each vertical andhorizontal one line can be used as the display area of the font.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit sets a backgroundcolor of a line in which the text data is not inputted as anintermediate color between a display color of the text data and anoriginally selected background color when an application for inputtingthe text data is executed.

Further another aspect of the present embodiment also relates to adisplay apparatus. This display apparatus is a display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes a luminancefor displaying the text data according to a display position of the textdata.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses andsystems may also be practiced as additional aspects of the presentinvention.

[Example of the Fifth Embodiment]

In the present embodiment, a cellular phone comprising an organic ELdisplay in a display screen as a display apparatus is considered. Thephosphor burn-in of the organic EL display can be reduced by changingdisplay form of a character string displayed on the cellular phone. Thesize or kind of the font of the character string to be displayed or thecolor thereof is changed when a user writes or reads an electric mailusing the cellular phone. The font used for display is also changed whenthe power of the cellular phone is turned on or off.

FIGS. 38A and 38B show a display screen in which the phosphor burn-in isarisen. In FIG. 38A, four characters “ABCD” are displayed in an area Aon the display screen. If these characters are displayed in the area Afor a long term, the four characters “ABCD” are seen as if thesecharacters are displayed there when an image in which all pixels aresame color is displayed, even if these characters are not displayed.That is, the phosphor burn-in is arisen in the area A.

When a character string is displayed on the display screen of thecellular phone, the character string is generally displayed on the samepart in many cases. Moreover, the character string is displayed fromupper left of the display screen in many cases, and it is not often thatthe character string is displayed on lower part of the display screen.Then, the font type of the character displayed on the display screen ischanged, or the luminance of the screen is changed according to the areaof the display screen.

The condition for changing the display form of the character string maybe (1) when the power of the display apparatus is turned on or off, (2)when the display apparatus is opened or closed in a case where thedisplay apparatus can be opened and closed like a fold-down typecellular phone, (3) when changing an application, (4) when a certainapplication, here, an e-mail application for example, is executed, (5)when there is no operation from a user for a predetermined term. In acase where the e-mail application is executed, the display form used maybe changed according to whether the e-mail is already read or not, orthe number of the characters included in the e-mail.

FIGS. 39A and 39B are figures showing a display screen in which acharacter string is displayed with two kinds of fonts different fromeach other. The font displayed in FIG. 39B is thin as a whole andinclines, compared with the font displayed in FIG. 39A. In FIG. 39A,five characters of the string are displayed on the fourth line, on theother hand, only one character of the string is displayed on the fourthline in FIG. 39B. An area where the character string is displayed may bechanged by changing the font. That is, the phosphor burn-in of thedisplay screen can be reduced by changing the kind of the font.

FIGS. 40A and 40B are figures showing a state where the size of the fontused is changed when the number of the characters displayed on thedisplay screen is different.

In FIG. 40A, 52 characters of alphabet from “A” to “Z” in a capital andsmall letter are displayed. On the other hand, in FIG. 40B, 26characters of alphabet from “A” to “Z” in only capital letter aredisplayed. In FIG. 40B, the number of the characters is decreased. Ifthe font of the same size as the font displayed in FIG. 40A is used, thecharacters are displayed on only half of the display screen. Then, thecharacter string can be displayed on the whole display screen byenlarging size of the font. Generally, when displaying a text and thelike, the character string is displayed from the upper left of thedisplay screen, and is not displayed on the bottom of the display screenin many cases. Then, text data can be displayed on the whole displayscreen by changing the size of the font.

Thereby, the case where only a part of the display screen is usedfrequently can be reduced, and the phosphor burn-in can be reduced.

FIG. 41 is a figure showing a state where a color of an area where acharacter string is not displayed is gradually changed from a backgroundcolor to a color same as the display color of the character string. Thecharacter string is displayed from the top to the fourth line. On theother hand, the character string is not displayed in the fifth toseventh lines. The color tone of these lines is gradually changed forevery line so that the color may not be changed extremely. All the linesin which the character string is not displayed may be displayed in thesame color, for example, an intermediate color between the color of thecharacter and the color of the background.

FIGS. 42A and 42B are figures showing a state where a Japanese isdisplayed in an area of 8*8 pixels. The pixels of the top row andrightmost column of this area is set up as a margin space so thatneighboring characters may not be touched. This area is also used as thedisplay area at the time of shifting the character. FIG. 42A shows astate before the character is shifted, and FIG. 42B shows a state wherethe character string is shifted one pixel to up and right, respectively.In the case where the character string consists of two or morecharacters, a character may be shifted one pixel to up, another right,or further another not shifted, for example, depending on the character.The phosphor burn-in can be reduced without spoiling display quantitygreatly.

The apparatus for realizing the above-mentioned change of the displayform of the character string and its operation are shown hereinafter.

FIG. 43 is a block diagram showing a basic structure of an organic ELdisplay apparatus 510. The organic EL display apparatus 510 isconstituted by an image source input unit 520, an e-mail attributeacquiring unit 524, an open-close detecting unit 552, an operationdetecting unit 554, an organic EL driving circuit 530, and an organic ELpanel 560.

The organic EL driving circuit 530 comprises an image adjusting unit 532which carries out various processings to a digital image signal inputtedfrom the image source input unit 520, an MPU (Micro Processing Unit) 534which calculates when these processings are carried out, and a DAC(Digital to Analog Converter) unit 542 which converts the image signalcarried out processing to an analog signal. The organic EL drivingcircuit 430 further comprises a text detecting unit 538, a luminancechanging unit 544, and a color changing unit 546. The organic EL drivingcircuit 538 further comprises a control signal generating unit whichgenerates various timing control signals and a memory which functions atable when actual processing is carried out, which are not shown in thefigure.

The image adjusting unit 532 performs an offset adjusting to adjust abrightness, a gain adjusting to adjust a contrast, and a processing toadjust input image signal which is performed gamma correction tovoltage-emitting luminance (V-T) characteristic of the organic EL panel.

When the display form of the character string is not changed, threekinds of the digital signals R_in, G_in, and B in are inputted from theimage source input unit 520 to the image adjusting unit 532. The imageadjusting unit 532 performs image adjusting processing like the offsetadjusting and the gain adjusting. The digital signals are outputted fromthe DAC unit 542 as three kinds of analog signals R_out, G_out, andB_out to the organic EL panel 560.

When the display form of the character string is changed, the change iscarried out by the structure shown below. The image adjusting unit 532comprises a text shifting unit 536 which shifts the character to use anarea where the character does not originally use among pixels whichconstitute the font as shown in FIG. 42.

The text detecting unit 538 detects the character string from theinputted digital image signal. The text detecting unit 538 changes thedisplay form of the detected character string in collaboration with theMPU 534 as shown in FIGS. 39 and 40. The luminance changing unit 544changes the luminance of the character according to a display positionthereof. The luminance changing unit 544 also changes the luminance inan area where the character string is not inputted as shown in FIG. 41.Similarly, the color changing unit 546 changes the color of thecharacter and the color of an area where the character string is notinputted.

The e-mail attribute acquiring unit 524 acquires an attribute of eache-mail when an e-mail application is executed. The attribute may be (1)whether the e-mail is already read or not, (2) the number of thecharacters included in the e-mail and the like.

The image source input unit 520 further comprises a text form changingunit 522. The text form changing unit 522 changes the display form ofthe character string displayed in the e-mail based on the attributeacquired by the e-mail attribute acquiring unit 524. The change of thedisplay form is also carried out by the text detecting unit 538, but thechange here is carried out before the digital image signal is inputtedto the organic EL driving circuit 524. The text detecting unit 538 maychange the display form of the character string based on the attributeof the e-mail acquired by the e-mail attribute acquiring unit 524.

The open-close detecting unit 552 detects open or close of the displayscreen in a case where the display screen of the cellular phone is afold-down type. The open-close detecting unit 552 instructs the MPU 534to change the display form of the character string used in the cellularphone when detecting. The operation detecting unit 554 instructs the MPU534 to change the display form of the character string used in thecellular phone when there is no operation to the cellular phone for apredetermined term.

In terms of hardware, this structure can be realized by a CPU, a memoryand other LSIs of an arbitrary computer. In terms of software, it isrealized by memory-loaded programs or the like having a function ofcontrolling display, but drawn and described here are functional blocksthat are realized in cooperation with those. Thus, it is understood bythe skilled in the art that these functional blocks can be realized in avariety of forms by hardware only, software only or the combinationthereof.

As mentioned-above, ccording to this embodiment, the generation of theluminance variation in the display screen can be reduced by changing thedisplay form of the character string and by changing the backgroundcolor of the display screen according to whether the character string isdisplayed or not. Moreover, the phosphor burn-in of the display screencaused by the concentration of the luminance variation can be reduced.

These embodiments have been given solely by way of illustration. It willbe understood by those skilled in the art that various modifications maybe made to combinations of the foregoing components and processes, andall such modifications are also intended to fall within the scope of thepresent invention.

[Effect of the Fifth Embodiment]

According to this embodiment, reduction of deterioration of the displayquality caused by the luminance variation is expectable. Moreover,reduction of the phosphor burn-in of the display screen caused by theconcentration of the luminance variation is also expected in anotherview point.

Although the present invention has been described by way of exemplaryembodiments, it should be understood that many changes and substitutionsmay be made by those skilled in the art without departing from thespirit and the scope of the present invention which is defined only bythe appended claims.

1. A display method wherein when displaying an image on a display areanarrower than an area which can be displayed, luminance data of anon-display area which does not display the image among the area whichcan be displayed is set as a guessed value of an average luminance ofthe image.
 2. A display apparatus comprising: an acquiring unit whichacquires a first image to be displayed; a first setting unit which setsa first area in which the first image is displayed and places the firstimage on the first area; and a second setting unit which sets, when thefirst area is smaller than an area which can be displayed, a secondimage to be displayed on a second area in which the first image is notdisplayed; wherein said second setting unit sets the second image in amanner where a guessed value of an average luminance of the first imageis substantially same as a guessed value of an average luminance of thesecond image.
 3. The display apparatus according to claim 2, whereinsaid second setting unit calculates the average luminance of the firstimage and sets the second image whose average luminance is substantiallysame as calculated average luminance of the first image on the secondarea.
 4. A display apparatus comprising: an acquiring unit whichacquires a first image to be displayed; a first setting unit which setsa first area in which the first image is displayed and places the firstimage on the first area; a second setting unit which sets, when thefirst area is smaller than an area which can be displayed, a secondimage to be displayed on a second area in which the first image is notdisplayed; a first storing unit which stores an accumulated averageluminance of the first image previously displayed on the first area; anda second storing unit which stores an accumulated average luminance ofthe second image previously displayed on the second area; wherein saidsecond setting unit sets the second image in a manner where theaccumulated average luminance of the second image approaches theaccumulated average luminance of the first image.
 5. The displayapparatus according to claim 2, wherein the second image is an image inwhich all pixels have substantially same luminance data.
 6. A mobileterminal which comprises an organic electroluminescence displayapparatus and can display an electric mail received or to be sent, themobile terminal comprising: an image processing circuit which can switcha display mode between a black character display mode in which acharacter part is displayed in black or a color with luminance lowerthan that of a background part and the background part is displayed inwhite or a color with luminance higher than that of the character part,and a white character display mode in which the background part isdisplayed in black or a color with luminance lower than that of thecharacter part and the character part is displayed in white or a colorwith luminance higher than that of the background part; and a controlcircuit which controls an operation of said image processing circuit;wherein said control circuit alternately switches the display modebetween the black character display mode and the white character displaymode.
 7. The mobile terminal according to claim 6, wherein said controlcircuit instructs a mode switch between the black character display modeand the white character display mode in accordance with a predeterminedrule.
 8. The mobile terminal according to claim 6, wherein said controlcircuit switches the mode between a display of a mail at the time ofmail creation, and a display of a mail which has already been receivedor transmitted.
 9. The mobile terminal according to claim 6, whereinsaid control circuit switches the mode for every one time orpredetermined number of times on the occasion of a display of a mail atthe time of mail creation.
 10. The mobile terminal according to claim 6,wherein said control circuit switches the mode for every one time orpredetermined number of times on the occasion of a display of a mailwhich has already been received or transmitted.
 11. The mobile terminalaccording to claim 6, wherein said control circuit switches the modebetween a display of a mail which has already been received, and adisplay of a mail which has already been transmitted.
 12. The mobileterminal according to claim 6, wherein said control circuit switches themode with a predetermined cycle.
 13. The mobile terminal according toclaim 6, wherein said control circuit switches the mode at a randomtiming.
 14. A display method of a specific picture which is displayed ona color organic EL display and a lighting part thereof increases ordecreases according to a situation, wherein the higher a probability oflighting of a part, the lower luminance of the part is set beforehand.15. The display method of the specific picture according to claim 14,wherein the specific picture is a picture showing an antenna and/or apicture showing residual quantity of a battery.
 16. A display method ofa specific picture which is displayed at areas which overlie each otheron a color organic EL display, in which two or three kinds of thespecific picture in roughly classification are switched and displayedaccording to a situation, wherein a dot which constitutes each specificpicture is set up in a manner where a color of an emitting elementturned on differs mutually among the two or three kinds of the specificpicture.
 17. The display method of the specific picture according toclaim 16, wherein the specific picture is a picture of an antenna whichis switched between a first picture showing an antenna bar and a secondpicture showing a character showing outside an area where an electricwave reaches according to a the situation.
 18. The display method of thespecific picture according to claim 16, wherein the specific picture isa picture showing residual quantity of a battery which is switchedbetween a first picture showing a bar showing the residual quantity ofthe battery and a second picture showing a character showing a chargeaccording to the situation.
 19. A display method of a plurality ofspecific pictures which is displayed on a color organic EL display,wherein the higher a frequency of displaying a pixel is, the lowerluminance of the pixel is set beforehand.
 20. A display apparatuscomprising: an optical element; a luminance information storing unitwhich stores luminance information set to said optical element; and adisplay changing unit which changes a display image displayed on saiddisplay apparatus in a manner where a guessed value of degradation ofeach optical element can be averaged based on the luminance informationstored.
 21. A display apparatus comprising: an optical element; and adisplay changing unit which changes a display image displayed on saiddisplay apparatus in a manner where a guessed value of degradation ofeach optical element can be averaged, maintaining an outline of thedisplay image.
 22. A display apparatus comprising: an optical element; adisplay screen which is composed of a plurality of display areas; and adisplay changing unit which changes a display image of each displayarea, maintaining an identity of a content of the display.
 23. Thedisplay apparatus according to claim 20, wherein said display changingunit changes the display image again, when a guessed value ofdegradation of said optical element reaches a predetermined value fromthe last change as a starting point.
 24. The display apparatus accordingto claim 20, wherein said display changing unit changes the displayimage, when an absolute value of an accumulated difference of aluminance of neighboring pixels exceeds a predetermined value.
 25. Thedisplay apparatus according to claim 20, wherein said display changingunit changes the display image, when a difference of a guessed value ofdegradation of said optical element in a row or a column of even numberand odd number exceeds a predetermined value.
 26. The display apparatusaccording to claim 20, wherein said display changing unit changes, whena power supply of said display apparatus is turned on or off, thedisplay image in a process of turning the power on or off.
 27. Thedisplay apparatus according to claim 20, wherein said display changingunit changes, when an application displayed on said display apparatus ischanged, the display image in a process of the change of theapplication.
 28. The display apparatus according to claim 20, whereinthe display screen of said display apparatus can be opened and closed,said display apparatus further comprising an opening-and-closingdetecting unit which detects opening or closing of the display screen;wherein said display changing unit changes the display screen whenopening and closing of the display screen are detected by saidopening-and-closing detecting unit.
 29. The display apparatus accordingto claim 20, wherein an operating unit for operating said displayapparatus is slide-type; said display apparatus further comprising aslide detecting unit which detects a slide of the operating unit;wherein said display changing unit changes the display screen when theslide of the operating unit is detected by said slide detecting unit.30. The display apparatus according to claim 20, wherein said displaychanging unit changes the display image by shifting a display positionof the display image.
 31. The display apparatus according to claim 20,wherein said display changing unit includes an area detecting unit whichdetects a specific area, the display position thereof is to be shifted,among an area of the display image; and said display changing unitchanges the display image by shifting the display position of thespecific area detected.
 32. The display apparatus according to claim 20,wherein said display changing unit adjusts a signal set up to eachoptical element according to a guessed value of degradation of saidoptical element.
 33. The display apparatus according to claim 32,wherein said display changing unit determines an amount of compensationto be given to a signal according to a value of the signal, whenadjusting the signal set up to said optical element.
 34. The displayapparatus according to claim 32, wherein said display changing unitdetermines an amount of compensation to be given to the signal based onthe guessed value of degradation of said optical element of asurrounding pixel, when adjusting the signal set up to said opticalelement.
 35. The display apparatus according to claim 20, wherein saiddisplay changing unit changes the display image by changing a displaycolor of each optical element.
 36. The display apparatus according toclaim 35, wherein said display changing unit changes the display imageby gradually changing luminosity ratio of said optical elementcorresponding to each color which constitutes a pixel.
 37. The displayapparatus according to claim 30, wherein a display area needed fordisplaying an actual display image is set up smaller than an effectivedisplay area which can be displayed in said display apparatus; and saiddisplay changing unit shifts the display area in the effective displayarea.
 38. The display apparatus according to claim 30, wherein saidoptical element corresponds to a dot, and a pixel includes dots of aplurality of colors, and said display changing unit shifts the displayimage per dot, and changes combination of said optical elements whichoriginally constitute one pixel.
 39. The display apparatus according toclaim 30, wherein in a case where the display image to be shiftedincludes a character, said display changing unit sets a margin spacewhich is originally set for displaying the character not to touch eachother as an area in which the arbitrary character can be shifted. 40.The display apparatus according to claim 30, wherein in a case where thedisplay image to be shifted includes a character, said display changingunit shifts the display image to a direction in which influence forreadability of the character is small when a user sees the character.41. The display apparatus according to claim 30, wherein said displaychanging unit scrolls the display image when there is no input from auser for predetermined period.
 42. The display apparatus according toclaim 30, wherein said display changing unit performs a mosaicprocessing to the display image and displays it when there is no inputfrom a user for predetermined period.
 43. The display apparatusaccording to claim 20, wherein said display changing unit selects, whena background image which functions as a wallpaper is newly set up, thewallpaper according to grade of degradation of said optical element. 44.A display method in a display apparatus which comprises an opticalelement, the method including: storing information of luminance set upto the optical element; and changing a display image displayed on thedisplay apparatus in a manner where a guessed value of degradation ofeach optical element can be averaged based on the luminance informationstored.
 45. A display method in a display apparatus which comprises anoptical element, the method including: changing a display imagedisplayed on the display apparatus in a manner where a guessed value ofdegradation of each optical element can be averaged, maintaining anoutline of the display image.
 46. A display apparatus comprising: anoptical element; and a display changing unit which changes display formof a text data displayed on said display apparatus in a manner where aguessed value of degradation of each optical element can be averaged;wherein said display changing unit changes, when a power supply of saiddisplay apparatus is turned on or off, the display form of the text datain a process of turning the power on or off.
 47. A display apparatuscomprising: an optical element; and a display changing unit whichchanges display form of a text data displayed on said display apparatusin a manner where a guessed value of degradation of each optical elementcan be averaged; wherein said display changing unit changes, when anapplication displayed on said display apparatus is changed, the displayform of the text data in a process of the change of the application. 48.A display apparatus comprising an optical element, a display screenthereof can be opened and closed, the display apparatus comprising: adisplay changing unit which changes display form of a text datadisplayed on said display apparatus in a manner where a guessed value ofdegradation of each optical element can be averaged; and anopening-and-closing detecting unit which detects opening or closing ofthe display screen; wherein said display changing unit changes thedisplay form of the text data when opening and closing of the displayscreen are detected by said opening-and-closing detecting unit.
 49. Adisplay apparatus comprising: an optical element; and a display changingunit which changes display form of a text data displayed on said displayapparatus in a manner where a guessed value of degradation of eachoptical element can be averaged; wherein said display changing unitchanges, when an electric mail is displayed on said display apparatus,the display form of the text data for every electric mail.
 50. A displayapparatus comprising: an optical element; and a display changing unitwhich changes display form of a text data displayed on said displayapparatus in a manner where a guessed value of degradation of eachoptical element can be averaged; wherein said display changing unitchanges, while a character input means comprised in said displayapparatus is operated for input of the character, the display form ofthe text data.
 51. A display apparatus comprising: an optical element;and a display changing unit which changes display form of a text datadisplayed on said display apparatus in a manner where a guessed value ofdegradation of each optical element can be averaged; wherein saiddisplay changing unit changes, when an electric mail is displayed, thedisplay form of the text data to be displayed according to whether theelectric mail has already been read or has not been read yet.
 52. Adisplay apparatus comprising: an optical element; and a display changingunit which changes display form of a text data displayed on said displayapparatus in a manner where a guessed value of degradation of eachoptical element can be averaged; wherein said display changing unitchanges the display form of the text data according to the number of thecharacter to be displayed when an electric mail is displayed.
 53. Thedisplay apparatus according to claim 46, wherein said display changingunit changes the display form of the text data by changing a font typeof the text data.
 54. The display apparatus according to claim 46,wherein said display changing unit shifts an arbitrary characterincluded in the text data using a margin space which is originally setto avoid displaying the characters touching each other.
 55. A displayapparatus comprising: an optical element; and a display changing unitwhich changes display form of a text data displayed on said displayapparatus in a manner where a guessed value of degradation of eachoptical element can be averaged; wherein said display changing unit setsa background color of a line in which the text data is not inputted asan intermediate color between a display color of the text data and anoriginally selected background color when an application for inputtingthe text data is executed.
 56. A display apparatus comprising: anoptical element; and a display changing unit which changes display formof a text data displayed on said display apparatus in a manner where aguessed value of degradation of each optical element can be averaged;wherein said display changing unit changes a luminance for displayingthe text data according to a display position of the text data.